chore(docs): Synology set-up guide (#16179)

* Addition of Synology set-up guide

* fix: format

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Co-authored-by: Alex <alex.tran1502@gmail.com>

docs/docs/install/synology.md

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+---
+sidebar_position: 85
+---
+
+# Synology [Community]
+
+:::note
+This is a community contribution and not officially supported by the Immich team, but included here for convenience.
+
+Community support can be found in the dedicated channel on the [Discord Server](https://discord.immich.app/).
+
+**Please report app issues to the corresponding [Github Repository](https://github.com/truenas/charts/tree/master/community/immich).**
+:::
+
+Immich can easily be installed on a Synology NAS using Container Manager within DSM. If you have not installed Container Manager already, you can install it in the Packages Center. Refer to the [Container Manager docs](https://kb.synology.com/en-us/DSM/help/ContainerManager/docker_desc?version=7) for more information on using Container Manager.
+
+## Step 1 - Download the required files
+
+Create a directory of your choice (e.g. `./immich-app`) to house Immich. In general, it's a best practice to have all Docker-based applications running under the `./docker` directory, so in this case, your directory structure will look like `./docker/immich-app`.
+
+Now create a `./postgres` and `./library` directory as sub-directories of the `./docker/immich-app`.
+
+When you're all done, you should have the following:
+
+- `./docker/immich-app/postgres`
+- `./docker/immich-app/library`
+
+Download [`docker-compose.yml`](https://github.com/immich-app/immich/releases/latest/download/docker-compose.yml) and [`example.env`](https://github.com/immich-app/immich/releases/latest/download/example.env) to your computer. Upload the files to the `./docker/immich-app` directory.
+
+## Step 2 - Populate the .env file with custom values
+
+Follow [Step 2 in Docker Compose](./docker-compose#step-2---populate-the-env-file-with-custom-values) for instructions on customizing the `.env` file, and then return back to this guide to continue.
+
+## Step 3 - Create a new project in Container Manager
+
+Open Container Manager, and select the "**Project**" action on the left navigation bar and then click "**Create**".
+![Create Project](../../static/img/synology-container-manager-create-project.png)
+
+In the settings of your new project, set "**Project name**" to a name you'll remember, such as _immich-app_. When setting the "**Path**", select the `./docker/immich-app` directory you created earlier. Doing so will prompt a message to use the existing `docker-compose.yml` already present in the directory for your project. Click "**OK**" to continue.
+
+![Set Path](../../static/img/synology-container-manager-set-path.png)
+
+The following screen will give you the option to further customize your `docker-compose.yml` file, giving you a warning regarding the `start_interval` property. Under the `healthcheck` heading, remove the `start_interval: 30s` completely and click "**Next**".
+
+![start interval](../../static/img/synology-container-manager-customize-docker-compose.png)
+
+Skip the section asking to set-up a portal for Web Station, and then complete the wizard which will build and start the containers for your project.
+
+Once your containers are successfully running, navigate to the "**Container**" section of Container Manager, right-click on the "**immich-server**" container, and choose the "**Details**".
+
+Scroll to the bottom of the "**Details**" section, and find the `IP Address` of the container, located in the `Network` section. Take note of the container's IP address as you will need it for **Step 4**.
+
+![Container Details](../../static/img/synology-container-manager-container-details.png)
+
+## Step 4 - Configure Firewall Settings
+
+Once your project completes the build process, your containers will start. In order to be able to access Immich from your browser, you need to configure the firewall settings for your Synology NAS.
+
+Open "**Control Panel**" on your Synology NAS, and select "**Security**". Navigate to "**Firewall**"
+
+![Firewall rules](../../static/img/synology-firewall-rules.png)
+
+Click "**Edit Rules**" and add the following firewall rules:
+
+- Add a "**Source IP**" rule for the IP address of your container that you obtained in Step 3 above
+- Add a "**Ports**" rule for the port specified in the `docker-compose.yml`, which should be `2283`
+
+## Next Steps
+
+Read the [Post Installation](/docs/install/post-install.mdx) steps or setup optional features below.
+
+### Setting up optional features
+
+- [External Libraries](/docs/features/libraries.md): Adding your existing photo library to Immich
+- [Hardware Transcoding](/docs/features/hardware-transcoding.md): Speeding up video transcoding
+- [Hardware-Accelerated Machine Learning](/docs/features/ml-hardware-acceleration.md): Speeding up various machine learning tasks in Immich