Docs restructure (#2953)

Needs to be merged into `gh-pages` later on.

docs/installation/docker/1_docker.md

@@ -0,0 +1,57 @@
+---
+title: Installation
+parent: Docker
+grand_parent: Installation
+has_toc: true
+nav_order: 1
+permalink: /installation/docker/install
+---
+
+# Installing Dendrite using Docker Compose
+
+Dendrite provides an [example](https://github.com/matrix-org/dendrite/blob/main/build/docker/docker-compose.yml) 
+Docker compose file, which needs some preparation to start successfully.
+Please note that this compose file only has Postgres as a dependency, and you need to configure
+a [reverse proxy](../planning#reverse-proxy).
+
+## Preparations
+
+### Generate a private key
+
+First we'll generate private key, which is used to sign events, the following will create one in `./config`:
+
+```bash
+mkdir -p ./config
+docker run --rm --entrypoint="/usr/bin/generate-keys" \
+  -v $(pwd)/config:/mnt \
+  matrixdotorg/dendrite-monolith:latest \
+  -private-key /mnt/matrix_key.pem
+```
+(**NOTE**: This only needs to be executed **once**, as you otherwise overwrite the key)
+
+### Generate a config
+
+Similar to the command above, we can generate a config to be used, which will use the correct paths
+as specified in the example docker-compose file. Change `server` to your domain and `db` according to your changes
+to the docker-compose file (`services.postgres.environment` values):
+
+```bash
+mkdir -p ./config
+docker run --rm --entrypoint="/bin/sh" \
+  -v $(pwd)/config:/mnt \
+  matrixdotorg/dendrite-monolith:latest \
+  -c "/usr/bin/generate-config \
+    -dir /var/dendrite/ \
+    -db postgres://dendrite:itsasecret@postgres/dendrite?sslmode=disable \
+    -server YourDomainHere > /mnt/dendrite.yaml"
+```
+
+You can then change `config/dendrite.yaml` to your liking.
+
+## Starting Dendrite
+
+Once you're done changing the config, you can now start up Dendrite with
+
+```bash
+docker-compose -f docker-compose.yml up 
+```