docs: Add Docker install guide

Based on Misskey's Docker guide:
https://github.com/misskey-dev/misskey-hub/blob/main/src/en/docs/install/docker.md

docs/install-docker.md

@@ -0,0 +1,70 @@
+# Create FoundKey instance with Docker Compose
+
+This guide describes how to install and setup FoundKey with Docker Compose.
+
+**WARNING:**
+Never change the domain name (hostname) of an instance once you start using it!
+
+
+## Requirements
+- Docker or Podman
+- Docker Compose plugin (or podman-compose)
+
+If using Podman, replace `docker` with `podman`. Commands using `docker compose` should be replaced with `podman-compose`.
+
+You may need to prefix `docker` commands with `sudo` unless your user is in the `docker` group or you are running Docker in rootless mode.
+
+## Get the repository
+```sh
+git clone https://akkoma.dev/FoundKeyGang/FoundKey.git
+cd FoundKey
+```
+
+##Configure
+
+Copy example configuration files with following:
+
+```sh
+cp .config/docker_example.yml .config/default.yml
+cp .config/docker_example.env .config/docker.env
+cp ./docker-compose.yml.example ./docker-compose.yml
+```
+
+Edit `default.yml` and `docker.env` according to the instructions in the files.
+
+Edit `docker-compose.yml` if necessary. (e.g. if you want to change the port).
+
+## Build and initialize
+The following command will build FoundKey and initialize the database.
+This will take some time.
+
+``` shell
+docker compose build
+docker compose run --rm web pnpm run init
+```
+
+## Launch
+You can start FoundKey with the following command:
+
+```sh
+docker compose up -d
+```
+
+## How to update your FoundKey server
+When updating, be sure to check the [release notes](https://akkoma.dev/FoundKeyGang/FoundKey/src/branch/main/CHANGELOG.md) to know in advance the changes and whether or not additional work is required (in most cases, it is not).
+
+```sh
+git stash
+git checkout master
+git pull
+git stash pop
+docker compose build
+docker compose stop && docker compose up -d
+```
+
+It may take some time depending on the contents of the update and the size of the database.
+
+## How to execute CLI commands
+```sh
+docker compose run --rm web node packages/backend/built/tools/foo bar
+```