Merge pull request #2956 from zackschuster/patch-1

add fsck error workaround to contributing.md

Author: jgonggrijp

CONTRIBUTING.md

@@ -15,3 +15,6 @@
 * Use the same coding style as the rest of the [codebase](https://github.com/jashkenas/underscore/blob/master/modules/index.js).
 
 * In your pull request, do not add documentation or re-build the minified `underscore-umd-min.js` file. We'll do those things before cutting a new release.
+
+### "Help, cloning fails with `fatal: fsck error in packed object`"
+This error is caused by zero-padded file modes in the commit history. As fixing this is highly destructive, we suggest ignoring these warnings. The simplest way is to instruct git to do so when cloning. For example, to clone from `jashkenas/underscore`, run the following command: `git clone --config transfer.fsckobjects=false git@github.com:jashkenas/underscore.git`. If cloning from a different user or organization, replace `jashkenas` with their name in the previous command.