Add doc/About.md describing the content of the doc/ directory, as well as

the procedure used when creating the new scans.

doc/About.md

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+# About the Scanned Manuals
+
+This directory's main content is scanned versions of the original German
+manuals of VolksForth from the 80s. There were 4 main flavours of VolksForth
+and accordingly 4 manuals: C64/C16/Plus4, Atari ST, CP/M and MSDOS.
+
+The manuals for C64/C16/Plus4, Atari ST and MSDOS have recently been rescanned
+and OCR-ed. Of the CP/M manual we have an older scan and an almost complete
+[Org Mode](https://orgmode.org/) transcript. A partial Org Mode transcript also
+exist of the MSDOS manual.
+
+Based on the different text versions of the different manuals (transscripts,
+sidecar files from `ocrmypdf`), a translation into an English manual is being
+started in the 6502/C64/doc directory for the C64 3.9.6 release. Eventually
+this is intended to result in a unified manual for all versions.
+
+Note: The mix of Org Mode and Markdown in documents here stems from different
+stems from different prefernces or past habits of different contributors.
+
+## VolksForth CBM 3.80 Manual
+
+The [doc/cbm/](cbm) directory contains the German manual for the C64/C16/Plus4
+VolksForth version 3.80.
+
+* [vf-cbm-380-manual-de.pdf](cbm/vf-cbm-380-manual-de.pdf) is the scanned and
+OCR-ed PDF.
+* [vf-cbm-380-manual-de.sidecar.txt](cbm/vf-cbm-380-manual-de.sidecar.txt)
+  is the sidecar text output generated by
+  [OCRmyPDF](https://github.com/ocrmypdf/OCRmyPDF)'s option `--sidecar`.
+* [raw-scans/](cbm/raw-scans) contains the raw PDF files as produced by the
+  scanner from the paper orignal.
+
+## VolksForth Atari ST 3.80 Manual
+
+The [doc/atari-st/](atari-st) directory contains the German manual for the
+Atari ST FolksForth version 3.80.
+
+* [vf-atari-st-380-manual-de.pdf](atari-st/vf-atari-st-380-manual-de.pdf) is
+  the scanned and OCR-ed PDF.
+* [vf-atari-st-380-manual-de.sidecar.txt](atari-st/vf-atari-st-380-manual-de.sidecar.txt)
+  is the sidecar text output generated by
+  [OCRmyPDF](https://github.com/ocrmypdf/OCRmyPDF)'s option `--sidecar`.
+* [raw-scans/](cbm/raw-scans) contains the raw PDF files as produced by the
+  scanner from the paper orignal.
+* [LIESMICH.TXT](atari-st/LIESMICH.TXT) is an overview, in German,
+  of VolksForth and of the files that come with the Atari ST version.
+  Note: The .SCR files are Forth screen files, i.e. sources, and they have
+  since been renamed to .FB (for Forth Block source).
+* [README.TXT](atari-st/README.TXT) is the same, in English.
+* [CHANGES.ORG](atari-st/CHANGES.ORG) is a change log, in German, between
+  versions 3.7 and 3.80.
+
+## VolksForth CP/M 3.80 Manual
+
+The [doc/cpm/](cpm) directory contains the German manual for the CP/M
+VolksForth version 3.80. Note that the CP/M VolksForth was shipped with the
+C64/C16/Plus4 manual, and the CP/M manual only describes the CP/M VolksForth's
+differences compared to the C64 etc. version.
+
+* [VolksForth-3.80-CPM.pdf](cpm/VolksForth-3.80-CPM.pdf) is the scanned
+  and OCR-ed PDF.
+* [readme.org](cpm/readme.org) is a transcript of the scanned PDF. Note that
+  the order of the chapters differ slightly between scan and transcript.
+
+## VolksForth MSDOS 3.81 Manual
+
+The [doc/msdos/](msdos) directory contains the German manual for the MSDOS
+VolksForth version 3.81.
+
+* [vf-msdos-381-manual-de.pdf](msdos/vf-msdos-381-manual-de.pdf) is the scanned
+  and OCR-ed PDF.
+* [vf-msdos-381-manual-de.sidecar.txt](msdos/vf-msdos-381-manual-de.sidecar.txt)
+  is the sidecar text output generated by
+  [OCRmyPDF](https://github.com/ocrmypdf/OCRmyPDF)'s option `--sidecar`.
+* [raw-scans/](msdos/raw-scans) contains the raw PDF files as produced by the
+  scanner from the paper orignal.
+* [LIESMICH.TXT](msdos/LIESMICH.TXT) is a partial transcript of the scanned
+  PDF.
+* [README.TXT](msdos/README.TXT) is a started cross-platform overview of
+  VolksForth, in English.
+
+## Scanning and OCR notes
+
+For the records, this is the procedure used to create the 3 newly-scanned PDFs:
+
+The scans were made from 3 printed manual copies in mint condition; the manuals
+are in A5 format.
+
+The scanner used is a HP Color LaserJet MFP M477fdn which has a document feeder
+with two-sided scanning ability, and a fixed A4 scanning size.
+Since a full VolksForth manual exceeds the capacity of the feeder,
+each manual was split into 3 batches; the resulting A4 PDFs are now sitting
+in the `raw-scans/` directories.
+
+The raw scans `scan0000.pdf` to `scan0002.pdf` were concatenated and cropped
+using the Linux GUI tool `pdfarranger` (version 1.4.2). Steps:
+* Drag & drop all files from `raw-scans/` into `pdfarranger` window.
+* Press ctrl-A to select all pages.
+* Edit -> Crop
+    * Set lower margin to 29% (1 - (1 / sqrt(2)).
+    * Set left and right margin to 14.5% (29% / 2).
+    * Click "OK.
+* Edit -> Edit Properties
+    * Set Creator to "Forth Gesellschaft e.V." (in other PDF vierers this is
+      displayed as the Author property).
+* Save as "newly-cropped.pdf"
+
+The final searchable PDF was created from the intermediate `newly-cropped.pdf`
+by adding an OCR text layer using OCRmyPDF:
+
+```
+ocrmypdf -l deu -d -c -i newly-cropped.pdfvf-<version>-manual-de.pdf --sidecar vf-<version>-manual-de.sidecar.txt
+```
+
+The sidecar file contains the OCR-ed text added into the text layer and is
+expected to be useful as input for a machine-aided translation of the manual
+into English.
+
+A note about PDF versions: The raw scans are PDF-1.4, `pdfarranger` outputs
+PDF-1.3 which seems to cause problems (error 14) when opening files with
+Adobe Acrobat. `ocrmypdf` produces PDF/A-2b which does not seem to cause these
+problems.