Improve plugin release process documentation (#233)

* first round of changes to plugin release process

* Add TOC

https://ecotrust-canada.github.io/markdown-toc/

* fix buy-in

* remove JIRA and fix formatting

* remove more JIRA

* Update plugins-release-process.md

* fix up to "Prepare Release"

* rest + udpate TOC

* fix toc

* fix toc

* release identifier

* simplify

* fixes

* try all the commands and fix along the way

* iterate

* fix list

* specify "Minor or Major version update"

* Update plugins-release-process.md

* iterate