Improve documentation page

* Move instructions on how to improve the docs to the bottom of the page.
* Promote using and customizing WET to be the top options.
* Use more direct language and links in first paragraph.
* Remove repetition of "Getting started".
Correct typos on bugs page
Correct typo on pull request page
Highlight the current stable version on the downloads page
Getting started improvements

* Move using and customizing WET to top
* Remove "Step 0" of creating a GitHub account, which is not needed in two out of four activities
* Improve clarity of instructions
Close unclosed strong tag
Merge pull request #5222 from jpmckinney/docs

Various documentation improvements