Add brief description of (current) chisel versioning and version recommendations. (#1180) (#1250)

* Add brief description of (current) chisel versioning and version recommendations.

* Respond to comments.
Replace "semantic versioning" with "a form of semantic versioning".

* Respond to comments - replace mmddyy with yyyymmdd.

* Mention change in SNAPSHOT naming.

(cherry picked from commit 041fd377)