Document how we obtain the name of the cabal config file.

Author: andreasabel

dist/index.js

@@ -16,6 +16,15 @@ async function cabalConfig(): Promise<string> {
     silent: true,
     listeners: {stdout: append, stderr: append}
   });
+  // The last line of the cabal help text is printing the config file, e.g.:
+  //
+  // > You can edit the cabal configuration file to set defaults:
+  // >   <<HOME>>/.cabal/config
+  //
+  // So trimming the last line will give us the name of the config file.
+  //
+  // Needless to say this is very brittle, but we secure this by a test
+  // in Cabal's testsuite:  https://github.com/haskell/cabal/pull/9614
   return out.toString().trim().split('\n').slice(-1)[0].trim();
 }