Fix contribute.md minor issues

Fixed link to readthedocs.org (it didn't work correctly in the site)
and changed the documentation forlder from doc to docs (according to
other changes I have proposed.)

Author: ktsiligkiris

docs/contributing.md

@@ -2,41 +2,43 @@
 
 ## Issues
 
-Report issues and suggest features and improvements on the
-[GitHub issue tracker](https://github.com/bbatsov/prelude/issues). Don't ask
-questions on the issue tracker - use the [support channels](support.md) instead.
+Report issues and suggest features and improvements on the [GitHub
+issue tracker](https://github.com/bbatsov/prelude/issues). Don't ask
+questions on the issue tracker - use the [support
+channels](support.md) instead.
 
-If you want to file a bug, please provide all the necessary info listed in
-our issue reporting template (it's loaded automatically when you create a
-new GitHub issue).
+If you want to file a bug, please provide all the necessary info
+listed in our issue reporting template (it's loaded automatically when
+you create a new GitHub issue).
 
 ## Patches
 
-Patches in any form are always welcome! GitHub pull requests are even better! :-)
+Patches in any form are always welcome! GitHub pull requests are even
+better! :-)
 
 Before submitting a patch or a pull request make sure that your patch
 is in line with the [contribution
 guidelines](https://github.com/bbatsov/prelude/blob/master/CONTRIBUTING.md).
 
 ## Documentation
 
-Good documentation is just as important as good code.
-Please, consider improving and extending this manual.
+Good documentation is just as important as good code.  Please,
+consider improving and extending this manual.
 
 ### Working on the Manual
 
 The manual is generated from the markdown files in the
-[doc](https://github.com/bbatsov/prelude/tree/master/doc) folder of Prelude's
-GitHub repo and is published to [Read the Docs](readthedocs.org). The
-[MkDocs](http://www.mkdocs.org/) tool is used to convert the markdown sources to
-HTML.
+[docs](https://github.com/bbatsov/prelude/tree/master/docs) folder of
+Prelude's GitHub repo and is published to [Read the
+Docs](https://readthedocs.org). The [MkDocs](http://www.mkdocs.org/)
+tool is used to convert the markdown sources to HTML.
 
-To make changes to the manual you simply have to change the files under
-`doc`. The manual will be regenerated automatically when changes to those files
-are merged in `master` (or the latest stable branch).
+To make changes to the manual you simply have to change the files
+under `docs`. The manual will be regenerated automatically when changes
+to those files are merged in `master` (or the latest stable branch).
 
-You can install `MkDocs` locally and use the command `mkdocs serve` to see the
-result of changes you make to the manual locally:
+You can install `MkDocs` locally and use the command `mkdocs serve` to
+see the result of changes you make to the manual locally:
 
 ```sh
 $ cd path/to/prelude/repo