Update the support page of z.cash

[lindanlee]

The links in the red can be consolidated. Elena is owning this, with Ryan making change to the site.

Discussion from slack:

• The user guide and integration guides are already in documentation, so I think it can easily be consolidated into a documentation tile. The main page of documentation has a quick start tile of pages, and those two are prominently featured so people won’t miss those.
• The download zcash client probably is best to be filed under documentation, since then people start with instructions, rather than do the github > rtd. It’s more direct. Similarly, the documentation presents links to github with how to get started on the specific stack, so it’s better to start there.
• practically, the “privacy and security” and “public keys” need to remain on the main website for strategic reasons / its importance.

[copernicus-mogley]

This will likely have to be pushed to next quarter and be done in parallel with z.cash site refresh which will largely consist of reorganizing content and navigation and requires collaboration/approval with/of Zcash Foundation.