Create PHS R packages.md

[Moohan]

We spoke about adding PHS package documentation to the Knowledge Base at the R-POD group meeting yesterday. This is my first draft of that.

• It probably needs a one-line / one-paragraph description of the package (I wonder if that could be pulled from the package DESCRIPTION?)
• I'm not sure if the table is the best way to present it...
• Links should probably be tidied so they're not just bare URLs.

[rmccreath]

Is it worth highlighting {phsverse} separately, my mental model at least thinks of things like that as fundamentally different. This could be a separate table to highlight "package suites", with a column to list packages included.

[Moohan]

@rmccreath Do you want to review this again, and if happy can you ping the next person too please!