Getting started > For developers content update

[klepas]

This is a PR for #58.

Primarily it:

• changes the direct HTML of example <link>s that linked to our staging minified files and instead links to them asking the user to download them
• overhauled/updated the a11y and browser support sections
• fixes the correct link and link text to the UI-Kit repo
• removes unnecessary semver info & expands on an abbreviation

Please review for both accuracy, and please consider word-smithing as needed/appropriate :)