Based on matrix-doc switching from master -> main and
MSCs being merged.

Our documentation has a history of using a document's name as a way to link to it, such as "See [workers.md]() for details". This makes sense when you're traversing a directory of files, but less sense when the files are abstracted away - as they are on the documentation website.

This PR changes the links to various documentation pages to something that fits better into the surrounding sentence, as you would when making any hyperlink on the web.

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Fixes #9778

ACME v1 has been fully decommissioned for existing installs on June 1st 2021(see https://community.letsencrypt.org/t/end-of-life-plan-for-acmev1/88430/27), so we can now safely remove it from Synapse.

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

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 Add a health warning making it clear that the 1711 upgrade FAQ is now out of date.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

fixes #4951

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

Fix incorrect heading level

A surprising number of people are using the well-known method, and are
simply copying the example configuration. This is problematic as the
example includes an explicit port, which causes inbound federation
requests to have the HTTP Host header include the port, upsetting some
reverse proxies.

Given that, we update the well-known example to be more explicit about
the various ways you can set it up, and the consequence of using an
explict port.

A surprising number of people are using the well-known method, and are
simply copying the example configuration. This is problematic as the
example includes an explicit port, which causes inbound federation
requests to have the HTTP Host header include the port, upsetting some
reverse proxies.

Given that, we update the well-known example to be more explicit about
the various ways you can set it up, and the consequence of using an
explict port.

MSC1711 certificates FAQ