Update the README to start taking content contributions (#99)

Fixes rdar://104089584

Author: amartini51

README.md

@@ -11,18 +11,13 @@ working with the community to extend Swift-DocC where needed.
 
 ## Contributing
 
-For now,
-we’re expecting most pull requests to be enhancements and bug fixes
-to support the Swift-DocC publication,
-with only minor content changes.
-
 For small changes,
 like typo fixes and changes to a few paragraphs,
 fork this repository and make a pull request.
 
 A formal contribution process for this document is still in development.
 In the meantime,
-start a thread in the [Swift forums][forum] for larger changes
+start a pitch thread in the [Swift forums][forum] for larger changes
 to discuss your approach and identify possible issues
 before you invest a lot of time in writing.