Improve Installation and Integration sections

[wolfgangwalther]

Both installation and integration are related - this is all about how PostgREST works together with other systems, no matter whether that's the operating system (installation) or other services (integrations).

The postgrest-docs repo had the following issues in this area still open:

Installation:

• [ ] https://github.com/PostgREST/postgrest-docs/issues/386
• [ ] https://github.com/PostgREST/postgrest-docs/issues/453
• [ ] https://github.com/PostgREST/postgrest-docs/issues/707
• [ ] https://github.com/PostgREST/postgrest-docs/issues/718
• [ ] Explain how to test whether the installation was successful.
• [ ] Explain how to take the next steps on configurating to get something useful.

Integrations:

• [ ] https://github.com/PostgREST/postgrest-docs/issues/203
• [ ] https://github.com/PostgREST/postgrest-docs/issues/229
• [ ] https://github.com/PostgREST/postgrest-docs/issues/474
• [ ] https://github.com/PostgREST/postgrest-docs/issues/475

[wolfgangwalther]

• [ ] We'll want to note in the installation section that the pre-compiled binaries from the release page need the proper dependencies installed to work (except the linux static, of course) and which those dependencies are. This came up in #3579