Add some basic code conventions to the README (#831)

docs/code-conventions.md

@@ -0,0 +1,13 @@
+# Code conventions for Dusk
+
+## Upstream when appropriate
+
+Bug fixes, documentation improvements, code cleanup, etc that also apply to the [original decompilation project](https://github.com/zeldaret/tp) should preferably be PR'd there.
+
+## Properly indicate Dusk-modified code
+
+When modifying original game code (i.e. in decomp) for Dusk's purposes, please clearly delineate such code as being Dusk-specific. Generally, this can be done by using `#if TARGET_PC` and keeping the original code in place. Use `#if AVOID_UB` for Undefined Behavior fixes to the original codebase.
+
+## Miscellaneous things
+
+* The original codebase makes heavy use of global `operator new` and similar overloads to allocate into a strict tree of heaps. This would cause many linkage headaches for us, so effectively all uses of `new` or `delete` in the original game code have been replaced with `JKR_NEW`, `JKR_DELETE`, or similar macros. See `JKRHeap.h` for the full list.