Created Feature coverage per architecture (markdown)

Feature-coverage-per-architecture.md

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+The following table shows which features are implemented for which CPU architecture. The table may contain mistakes.
+
+feature | 6502 | Z80
+--|--|--
+`+'`, `-'`, `+'=`, `-'=`    | 📺 | ✔️
+`*`, `*=`            | ✔️ | 🐌
+`*'`, `*'=`          | 📺 | ❌
+`>>>>`               | ✔️ | ❌
+`<<'`, `<<'=`        | 📺 | ❌
+`>>'`, `>>'=`        | ✔️ | ❌
+signed comparisons   | ⚠️ | ❌
+return dispatch      | ✔️ | ❌
+other features       | ✔️ | ✔️
+
+##### Legend:
+
+✔️ – implemented  
+📺 – implemented only for subarchitectures that support it natively  
+🐌 – implemented, but suboptimal  
+⚠️ – implemented, but incorrectly  
+❌ – not implemented yet  
+
+#### Further remarks
+
+* 65816 code is quite suboptimal. If you're targeting a 65816 machine only, consider using something else for the time being.
+
+* Intel 8080 and Gameboy support added right now would mean no support for stack variables.
+
+* CPU's from the 6800 and 8086 families can be added in the future.