Fixed return dispatch returns on LUnix. Added non-relocated address constants.

docs/api/target-platforms.md

@@ -81,6 +81,17 @@ After putting it on a disk, the file can be run with:
     
 Currently, multipart BBC Micro programs are not supported.
 
+### A note about LUnix
+
+LUnix uses relocatable code, which means that object addresses (`.addr`) are not constants. 
+To help with this problem, new constants are defined, with a `.rawaddr` suffix. 
+They are not relocated, so to use them, you need to manually relocate them 
+by adding `relocation_offset` to their high bytes:
+
+    pointer p
+    p = variable.rawaddr
+    p.hi += relocation_offset
+
 ## Adding a custom platform
 
 Every platform is defined in an `.ini` file with an appropriate name.