Dendrite Documentation Fix (#2913)

### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->
I was reading through the Dendrite documentation on
https://matrix-org.github.io/dendrite/development/contributing and
noticed the installation link leads to a 404 error. This link works fine
if it is viewed directly from
[docs/CONTRIBUTING.md](https://github.com/matrix-org/dendrite/blob/main/docs/CONTRIBUTING.md)
but this might not be very obvious to new contributors who are reading
through the [contribution
page](https://matrix-org.github.io/dendrite/development/contributing)
directly.

This PR is mainly a small re-organization of the online documentation
mainly in the
[Development](https://matrix-org.github.io/dendrite/development) tab
along with any links throughout the doc that may be impacted by the
change. This does not contain any Go unit tests as this does not
actually touch core dendrite functionality.

* [ ] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off below using a legally
identifiable
name](https://matrix-org.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

Signed-off-by: `Kento Okamoto <kentokamoto@proton.me>`

docs/FAQ.md

@@ -91,7 +91,7 @@ Please use PostgreSQL wherever possible, especially if you are planning to run a
 ## Dendrite is using a lot of CPU
 
 Generally speaking, you should expect to see some CPU spikes, particularly if you are joining or participating in large rooms. However, constant/sustained high CPU usage is not expected - if you are experiencing that, please join `#dendrite-dev:matrix.org` and let us know what you were doing when the
-CPU usage shot up, or file a GitHub issue. If you can take a [CPU profile](PROFILING.md) then that would
+CPU usage shot up, or file a GitHub issue. If you can take a [CPU profile](development/PROFILING.md) then that would
 be a huge help too, as that will help us to understand where the CPU time is going.
 
 ## Dendrite is using a lot of RAM
@@ -99,7 +99,7 @@ be a huge help too, as that will help us to understand where the CPU time is goi
 As above with CPU usage, some memory spikes are expected if Dendrite is doing particularly heavy work
 at a given instant. However, if it is using more RAM than you expect for a long time, that's probably
 not expected. Join `#dendrite-dev:matrix.org` and let us know what you were doing when the memory usage
-ballooned, or file a GitHub issue if you can. If you can take a [memory profile](PROFILING.md) then that
+ballooned, or file a GitHub issue if you can. If you can take a [memory profile](development/PROFILING.md) then that
 would be a huge help too, as that will help us to understand where the memory usage is happening.
 
 ## Dendrite is running out of PostgreSQL database connections

docs/development/CONTRIBUTING.md

@@ -9,7 +9,7 @@ permalink: /development/contributing
 Everyone is welcome to contribute to Dendrite! We aim to make it as easy as
 possible to get started.
 
- ## Contribution types
+## Contribution types
 
 We are a small team maintaining a large project. As a result, we cannot merge every feature, even if it
 is bug-free and useful, because we then commit to maintaining it indefinitely. We will always accept:
@@ -57,7 +57,7 @@ to do so for future contributions.
 
 ## Getting up and running
 
-See the [Installation](installation) section for information on how to build an
+See the [Installation](../installation) section for information on how to build an
 instance of Dendrite. You will likely need this in order to test your changes.
 
 ## Code style
@@ -151,7 +151,7 @@ significant amount of CPU and RAM.
 
 Once the code builds, run [Sytest](https://github.com/matrix-org/sytest)
 according to the guide in
-[docs/sytest.md](https://github.com/matrix-org/dendrite/blob/main/docs/sytest.md#using-a-sytest-docker-image)
+[docs/development/sytest.md](https://github.com/matrix-org/dendrite/blob/main/docs/development/sytest.md#using-a-sytest-docker-image)
 so you can see whether something is being broken and whether there are newly
 passing tests.