Update hacking.md, fixes #177

Author: hasufell

.ghci

@@ -13,9 +13,7 @@ that must evaluate to `True`. These tests follow a few rules:
 * If `Valid x =>` appears at the start of a doc test, that means the property
   will only be tested with `x` passing the `isValid` predicate.
 
-The tests can be generated by `make gen` in the root of the repo, and will be placed in `tests/TestGen.hs`.
+The tests can be generated by `make gen` in the root of the repo, and will be placed in `tests/filepath-tests/TestGen.hs`.
 The `TestGen.hs` file is checked into the repo, and the CI scripts check that `TestGen.hs` is in sync with
 what would be generated a fresh - if you don't regenerate `TestGen.hs` the CI will fail.
 
-The `.ghci` file is set up to allow you to type `ghci` to open the library, then `:go` will regenerate the
-tests and run them.