Various documentation improvements

The goal of this pull request is to make it easier for people to adopt WET.

For example, the "Getting Started" page started with "reporting a bug". I think most people who want to "get started" with WET are looking to **use it**. The next mostly likely action is to customize WET to fit their design better. Two things I couldn't change:

* [ ] "Communications material" does not belong under "Documentation". Please put it on its own page.
* [ ] "I want to report a bug or ask a question about WET" doesn't tell you how to ask a question about WET.

Summary of commits:

* 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".
* 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
* Highlight the current stable version on the downloads page
* Correct typo on pull request page
* Correct typos on bugs page