Remove mention of experimental branch

Also mention why the maintenance branch exists.
Remove incorrect comment in workflow
Remove contents comments
Remove "Where to Start?" section

Incorporate some of it into the intro text.
Remove "Installing Freeseer" page

The Quick Start guide does a good job of covering the installation
process. Having multiple places where we discuss the same thing is
confusing for the user and more for us to maintain.

Also removed some junk such as comments.
Remove "Technical Writer" page

Not necessary. The readme of the freeseer-docs repo does a good job
introducing the documentation tools and how to get started.

Note that the documentation.rst page also mentioned sending in
documentation patches by email (for those who weren't comfortable
with Git or GitHub). I'm sure we'll still allow this, but it's never
happened so far, so we can safely remove the mention of it.
Rewrite Designers page

- Remove tool recommendations;
  Experienced designers will have their own preferences

- Include graphic designers

- More concise wording
Merge "Power Users" page with "Designers" page

They're both very short, so might as well combine them.
Improve Student's "Getting Started" section

- Clearer steps

- Add missing steps
Add new section about the sprint
Rewrite "Deciding What to Work On" section

- Remove content that didn't belong

- Give more details about what can be worked on

- Mention translations as a minor project
Rewrite "Stay in Touch" section

- Renamed to "Communicate"

- Removed analogy and fluff

- Be specific about communication expectations
Improve "Expectations" and remove "How to Succeed"

- Be more clear with some expectations and add new ones

- "How to Succeed" was basically covered in other sections
Improve steps to add a translation

- Also fix link to Qt Linguist manual
Improve steps for updating translation resources

And use headings that aren't a part of the ToC.
Fix link to translation, use document reference
Add image to aid with changing sharing settings