Update docs/configuring-well-known.md and docs/installing.md (#3767)

* Update docs/configuring-well-known.md: remove redundant information

For example, anchor links to the headers are distractive as these headers are displayed by scrolling a bit.

Also: edit section headers

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: add "Support service discovery" as a type of well-known service discovery

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: recategorize the sections about installing well-known files on the base domain's server

The commit merges the content of the option 2 with the section above, as both explain how to serve the base domain via the playbook and claim it is the easy way of installing well-known files, and therefore the content is repetitive.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: create a section for types of well-known service discovery mechanism

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: add a link to the Matrix Specification, to which MSC 1929 was implemented

MSC 1929 has no longer been for an early adopter.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: iterate

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-base-domain-serving.md

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* Update docs/configuring-well-known.md

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

* Update docs/installing.md: iterate

Summary:
- Try to reflect review comments
- Declare that the shorter user identifier is recommended
- Add a note about installing the server matrix.example.com directly, with the link to the FAQ entry

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/installing.md: replace the anchor link to docs/configuring-well-known.md with one to docs/howto-server-delegation.md

Service Discovery via .well-known files is one of the two ways for server delegation, and it is possible to set up server delegation via a DNS SRV record instead (though it is more advanced and complicated), so it should be more proper to use the words "delegation/redirection" than "service discovery".

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-well-known.md: fix a typo

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

---------

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Slavi Pantaleev <slavi@devture.com>

docs/configuring-playbook-base-domain-serving.md

@@ -22,7 +22,7 @@ Doing this, the playbook will:
 
 - obtain an SSL certificate for the base domain, just like it does for all other domains (see [how we handle SSL certificates](configuring-playbook-ssl-certificates.md))
 
-- serve the `/.well-known/matrix/*` files which are necessary for [Federation Server Discovery](configuring-well-known.md#introduction-to-client-server-discovery) (also see [Server Delegation](howto-server-delegation.md)) and [Client-Server discovery](configuring-well-known.md#introduction-to-client-server-discovery)
+- serve the `/.well-known/matrix/*` files which are necessary for [Federation Server Discovery](configuring-well-known.md#federation-server-discovery) (also see [Server Delegation](howto-server-delegation.md)) and [Client-Server discovery](configuring-well-known.md#client-server-discovery)
 
 - serve a simple homepage at `https://example.com` with content `Hello from example.com` (configurable via the `matrix_static_files_file_index_html_template` variable). You can also [serve a more complicated static website](#serving-a-static-website-at-the-base-domain).