docs(a11y): add a list of supported screen readers

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Enhancement
[x] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Our docs say that we build "accessible UI components" but we don't specify any further details.

Issue Number:
Fixes #11449

What is the new behavior?

• add a list of supported screen readers to docs site
• add screen reader field to issue template
• update browser support table
• update README.md
  • require AngularJS 1.7.2+
  • remove out of date http://browserl.ist link and image since their site is down
  • link to screen reader support section on docs site
  • update docs site screenshot
  • add missing step to install Gulp v3 globally
  • update versions in examples to use 1.2.0

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[andrewseguin]

LGTM - there are several nits of formatting on the README that just seem to be due to your formatter, e.g. line breaks that put a word on the next line even though there is more than enough room for it on the previous line (see line 213 for example)