Simplify README

The UCI protocol is rather technical and has little value in our README. Instead
it should be explained in our wiki. "Contributing" is moved above "Compiling
Stockfish" to make it more prominent.

Also move the CONTRIBUTING.md into the root directory and include it in the
distributed artifacts/releases.

closes https://github.com/official-stockfish/Stockfish/pull/4766

No functional change

.github/workflows/stockfish_arm_binaries.yml

@@ -128,6 +128,7 @@ jobs:
           cp AUTHORS stockfish/
           cp CITATION.cff stockfish/
           cp README.md stockfish/
+          cp CONTRIBUTING.md stockfish/
           tar -cvf stockfish-android-$BINARY.tar stockfish
 
       - name: Upload binaries

.github/workflows/stockfish_binaries.yml

@@ -161,6 +161,7 @@ jobs:
           cp AUTHORS stockfish/
           cp CITATION.cff stockfish/
           cp README.md stockfish/
+          cp CONTRIBUTING.md stockfish/
 
       - name: Create tar
         if: runner.os != 'Windows'