Added module change database

README.rst

@@ -13,3 +13,10 @@ Build with:
 .. code::
 
    cabal build -w /path/to/ghc/HEAD/_build/stage1/bin/ghc
+
+ghc-api.csv
+===========
+
+ghc-api.csv is a file chronicling GHC's module renamings. Right now it duplicates information from ghc-api-compat.cabal, and there's no guarantee that it will be kept up-to-date or in sync, but there's an aspiration that this package(and others) can be generated automatically from it, and it can serve as a 'single source of truth'.
+
+Please note modules may have been renamed multiple times. In that case, there will be multiple entries, from A to B and from B to C.
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