Some small fixes to the copy in #6907.

Co-Authored-By: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

... and update INSTALL.md to include py3.8.

We'll also have to update the buildkite pipeline to run it

Converting some of the rst documentation to markdown.  Attempted to
preserve whitespace and line breaks to minimize cosmetic change.

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Fixes #4901

Add FAQ questions to federate.md. Add a health warning making it clear that the 1711 upgrade FAQ is now out of date.

1.0 upgrade/install notes

* Stop telling people to install the optional dependencies.

They're optional.

Also update the postgres docs a bit for clarity(?)

We don't ship jessie packages, so these were a bit misleading.

* Use packages.matrix.org for packages

See https://github.com/vector-im/riot-web/issues/9497 (applies to more than just Olm)

* changelog

Improved federation configuration docs.  Specifically detailing  .well-known and SRV based delegation methods. 

Inspiration Valentin Lab <valentin.lab@kalysto.org> for https://github.com/matrix-org/synapse/pull/4781

* Clarify what registration_shared_secret allows for (#2885)

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Lots of updates to the README/INSTALL.md.

Fixes #4601.

Factor out the reverse proxy info to a separate file, add some more info on
reverse-proxying the federation port.

The readme was getting pretty unmanageable and hard to grok. This is an attempt to simplify things by moving installation instructions from the README to a separate file. I've tried to resist the temptation to fix too much stuff while I'm here - it mostly just copies-and-pastes from one doc to the other, and changes from rst to md syntax.