docs: Add build page; correct proxy info; fix Caddy example (#2579)

* Add build page; correct proxy info; fix Caddy example

* Improve Caddyfile example

* Apply review comments; add polylith Caddyfile

docs/installation/10_starting_polylith.md

@@ -0,0 +1,73 @@
+---
+title: Starting the polylith
+parent: Installation
+has_toc: true
+nav_order: 10
+permalink: /installation/start/polylith
+---
+
+# Starting the polylith
+
+Once you have completed all of the preparation and installation steps,
+you can start your Dendrite polylith deployment by starting the various components
+using the `dendrite-polylith-multi` personalities.
+
+## Start the reverse proxy
+
+Ensure that your reverse proxy is started and is proxying the correct
+endpoints to the correct components. Software such as [NGINX](https://www.nginx.com) or
+[HAProxy](http://www.haproxy.org) can be used for this purpose. A [sample configuration
+for NGINX](https://github.com/matrix-org/dendrite/blob/main/docs/nginx/polylith-sample.conf)
+is provided.
+
+## Starting the components
+
+Each component must be started individually:
+
+### Client API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml clientapi
+```
+
+### Sync API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml syncapi
+```
+
+### Media API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml mediaapi
+```
+
+### Federation API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml federationapi
+```
+
+### Roomserver
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml roomserver
+```
+
+### Appservice API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml appservice
+```
+
+### User API
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml userapi
+```
+
+### Key server
+
+```bash
+./dendrite-polylith-multi -config /path/to/dendrite.yaml keyserver
+```