Docs: Use something other than the document name to describe a page (#10399)

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.

docs/setup/installation.md

@@ -412,7 +412,7 @@ instead. Advantages include:
 - allowing the DB to be run on separate hardware
 
 For information on how to install and use PostgreSQL in Synapse, please see
-[docs/postgres.md](../postgres.md)
+[Using Postgres](../postgres.md)
 
 SQLite is only acceptable for testing purposes. SQLite should not be used in
 a production server. Synapse will perform poorly when using
@@ -427,7 +427,7 @@ over HTTPS.
 
 The recommended way to do so is to set up a reverse proxy on port
 `8448`. You can find documentation on doing so in
-[docs/reverse_proxy.md](../reverse_proxy.md).
+[the reverse proxy documentation](../reverse_proxy.md).
 
 Alternatively, you can configure Synapse to expose an HTTPS port. To do
 so, you will need to edit `homeserver.yaml`, as follows:
@@ -454,7 +454,7 @@ so, you will need to edit `homeserver.yaml`, as follows:
   `cert.pem`).
 
 For a more detailed guide to configuring your server for federation, see
-[federate.md](../federate.md).
+[Federation](../federate.md).
 
 ### Client Well-Known URI
 
@@ -566,9 +566,7 @@ on your server even if `enable_registration` is `false`.
 ### Setting up a TURN server
 
 For reliable VoIP calls to be routed via this homeserver, you MUST configure
-a TURN server. See
-[docs/turn-howto.md](../turn-howto.md)
-for details.
+a TURN server. See [TURN setup](../turn-howto.md) for details.
 
 ### URL previews