docs: wrote part about contributing

Author: sourcehold

docs/contributing.rst

@@ -1,3 +1,4 @@
+=======================
 Contributing to OpenSHC
 =======================
 
@@ -36,3 +37,31 @@ Ready to dive in? Here's how you can start contributing to OpenSHC.
    reccmp-reccmp --paths "path\to\Stronghold Crusader.exe" "build\OpenSHC.dll" "build\OpenSHC.pdb" .
 
 
+Developing contributions
+=========================
+
+Contributions are done by contributing either:
+
+* reimplemented source code for functions of the original game.
+* data structures.
+* other code.
+
+Contributing functions
++++++++++++++++++++++++
+
+The functions of the original game are referenced by address.
+
+The 1.41 Latin version of the Stronghold Crusader.exe is used as the reference version.
+
+For example, the function that checks if X and Y coordinates are valid coordinates lives at address 0x401000.
+
+Since the names of functions and variables may change (improve), you can refer to the function using the address instead.
+
+Compilation
+++++++++++++
+
+When compiling OpenSHC, the addresses are resolved for the build target.
+For example, if OpenSHC is being compiled for Extreme, the addresses resolve to the address for the Stronghold_Crusader_Extreme.exe
+
+In order to make explicit which version you are referring to, or in case a function does not exist in the reference version, you can use the ``shce::0x401000`` syntax.
+Note that the part between `::` is for specifying a specific hash if necessary, e.g. ``shc:92fac0d0:0x401000``