Clarified the documentation README [ci skip]

The documentation README was previously intended to be read from
the documentation repository, not from the source repository.
This had the potential to give off the impression that documentation
pull requests were not allowed, when exactly the opposite is the
case.  The README has been improved to make it more clear how to
contribute pull requests to update the documentation.

Thanks to Brent Connor [1] for pointing out this issue over at
Stack Overflow [2].

[1]: https://stackoverflow.com/users/3954106/brent-connor
[2]: http://stackoverflow.com/q/28705192/359284

docs/README.md

@@ -1,18 +1,24 @@
 Select2 Documentation
 =====================
-This repository holds the latest documentation for [Select2][select2].
+[This repository][select2-docs-source] holds the latest documentation for
+[Select2][select2].
 
 What is this?
 -------------
-
 The documentation is automatically extracted from the `docs` directory at the
 [Select2 source repository][select2-source]. This is done periodically by
 the maintainers of Select2.
 
-**Pull requests will usually be ignored, documentation fixes should be made in
-the source repository.** We _may_ accept pull requests if they match the
-source `docs` directory, but for the most part pull requests will be closed on
-sight.
+How can I fix an issue in these docs?
+-------------------------------------
+If you are reading this from the source repository, within the `docs` directory,
+then you're already in the right place. You can fork the source repository,
+commit your changes, and then make a pull request and it will be reviewed.
+
+**If you are reading this from the
+[documentation repository][select2-docs-source], you are in the wrong place.**
+Pull requests made directly to the documentation repository will be ignored and
+eventually closed, so don't do that.
 
 How can I build these docs manually?
 ------------------------------------
@@ -28,4 +34,5 @@ Which will start up the documentation on port 4000. You will need
 
 [jekyll]: http://jekyllrb.com/
 [select2]: https://select2.github.io
+[select2-docs-source]: https://github.com/select2/select2.github.io
 [select2-source]: https://github.com/select2/select2