Add JSON examples to the contributing guidelines

* Add JSON examples for Resources and Learning Validations
* Add guidelines for contributing books/ebooks for App Store compliance
* Add clarifying comments on ID autogeneration

Minor:
* Add headers to sections

CONTRIBUTING.md

@@ -9,12 +9,53 @@ Contributing
 * Use the present tense in commit messages
 * Shorten commit messages to 50 characters with bulleted details
 
-
 > In which format should my contributions be submitted?
 
 * Pull requests should be in JSON format
-* Run the validator script (`rake validate`)
-* For more detailed output, use [JSONlint.com](http://jsonlint.com).
+* Resources should be of the format:
+
+```
+{
+    "title": "Read Learn Objective-C on the Mac",
+    "uri": "http://amzn.to/learn-objective-c-mac",
+    "publisher": "http://www.apress.com/9781430218159",
+    "ibook": "itms-books://itunes.apple.com/us/book/learn-objective-c-on-the-mac/id492011030?mt=11"
+}
+```
+See [example trails](trails/unix.json).
+
+
+Book Resources (e.g. print and e-books)
+---------------------------------------
+
+* Book resources only have to include a "publisher" link if the "uri" is an Amazon link.
+* If the book is available in the iBookstore, include the link under "ibooks" and replace the `https` prepended protocol with `itms-books` as in the above example.
+
+Learning Validations
+--------------------
+
+* Learning Validations should be of the format:
+
+```
+{
+    "title": "Define a method."
+},
+{
+    "title": "Invoke a method."
+}
+```
+
+Unique ID generation
+--------------------
+
+* A resource or validation's id will be generated when `rake` is run. Do not
+  generate these yourself.
+
+Validating JSON
+---------------
+
+* Run the tests, ID generator, and validator with `rake`
+* For more detailed debugging, use [JSONlint.com](http://jsonlint.com).
 * Considering using [this regex](https://gist.github.com/4068038) for converting Markdown to JSON
 
 Merging Pull Requests (for admins)