Update README.md

`libgit2` does this and I think this fixes it without having to re-build everything.

Update README.md

README.md

@@ -145,7 +145,10 @@ latest version.
  b. To delete existing binaries of `julia` and all its dependencies,
  delete the `./usr` directory _in the source tree_.
 
-3. In extreme cases, you may wish to reset the source tree to a pristine state.
+3. If you've moved the source directory, you might get errors such as
+ ```CMake Error: The current CMakeCache.txt directory ... is different than the directory ... where CMakeCache.txt was created.```, in which case you may delete the offending dependency under `deps`
+
+4. In extreme cases, you may wish to reset the source tree to a pristine state.
  The following git commands may be helpful:
 
  ```sh
@@ -155,6 +158,8 @@ latest version.
 
  _To avoid losing work, make sure you know what these commands do before you
  run them. `git` will not be able to undo these changes!_
+ 
+
 
 <a name="Uninstalling-Julia"/>
 ## Uninstalling Julia