Updates to the browser support md doc.

[klepas]

Description

Updates the browser doc page:

• Removes line re. updating when user needs change (because we should be doing that anyway)
• Changes the line that the browser support levels were drawn from the analytics data (not quite right) to note that this doc has drawn on that data generally.
• Updates the test status of mobile and desktop browser tables
• Adds a line that we list common browsers/devices and their test status, but not unsupported devices (there was some prev. confusion over the tablets being the ‘supported’ ones, and then saying we don’t list the supported/unsupported seemed confusing).
• Removes the snippet at the end re. the decision for us not to pursue a browser decision tree (something the BBC came up with). This has caused confusion (what is a browser decision tree?), esp. since we don’t link to one; removing.

This PR seeks to address https://github.com/AusDTO/gov-au-ui-kit/issues/431, at least in part.

Question…

I think it’s important to move some of this data over into the design guide website. Thoughts?

Definition of Done

• [x] Content/documentation reviewed by Julian or someone in the Content Team
• [x] Reviewed by one of the core developers
• [x] CHANGELOG updated

[klepas]

@dominikwilkowski I wanna merge this before releasing today.

Thoughts?

[dominikwilkowski]

I've already approved the PR.

[klepas]

@dominikwilkowski I guess I was asking if you were OK merging despite not having yet had Jools’ review?

[klepas]

I can has merge plz? (:

[joolswood]

Thanks @klepas all these of these changes are sane and helpful.

I expect that there will be interest in seeing information from the browser support doc directly on Design Guide site (link seems a bit buried here http://design-guide.apps.staging.digital.gov.au/getting-started/developers/index.html#browser-support on reflection). Can we do some user research to figure out what/where people need this? That's kinda what I was getting at with #431