update docs for 0.12.2 changes

(cherry picked from commit e6e60c4fa848d1c9ce1349eff750cfa2faf156dc)
Readme + Changelog for 0.12.2

(cherry picked from commit 7468f092ae08d6d184175432d38d64d4ea4ec02a)
v0.12.2 blog post

(cherry picked from commit 2f6a95d5a214bd0145c864604bc884c73ee6f865)
0.12.2 starter kit

(cherry picked from commit 6c5cb72cdc344e561fde6609b83c91f945127897)