Add a building from source doc for Firezone (#1078)

* Add a building from source doc for Firezone

* Apply suggestions from code review

Co-authored-by: Jamil <jamilbk@users.noreply.github.com>
Signed-off-by: Andrew Rousset <andrew@firezone.dev>

Signed-off-by: Andrew Rousset <andrew@firezone.dev>
Co-authored-by: Jamil <jamilbk@users.noreply.github.com>

docs/docs/deploy/advanced/build-from-source.mdx

@@ -0,0 +1,88 @@
+---
+title: Build From Source
+sidebar_position: 1
+---
+
+Building from source allows you to bring Firezone to unsupported platforms.
+
+:::warning
+You're entering unsupported territory. This is not for the faint of heart and
+will require being able to figure out snags you may hit on your own.
+
+If you're very comfortable with your environment of choice, then read on to
+learn how to build Firezone from source.
+:::
+
+:::info
+You will need to setup your own service management for Firezone (eg. `runit`,
+`systemd`, shell scripts). You will also need to install and configure your
+own database (eg. `postgres`) and reverse proxy (eg. `caddy`, `nginx`).
+
+Info about database configuration is [here](../external-database/#configure-firezone-to-connect),
+and info about configuring a reverse proxy is [here](../reverse-proxy/#proxy-requirements).
+:::
+
+# Prerequisites
+
+:::info
+Check the `.tool-versions` file [here](https://github.com/firezone/firezone/blob/master/.tool-versions)
+for the versions we use for Erlang, Elixir, and Node. If your system supports it,
+you can install these using [asdf-vm](https://asdf-vm.com/guide/getting-started.html)
+using a similar `.tool-versions` of your own to match versions. Your system's package
+manager may have them as well.
+:::
+
+**These must be available in the user's path that runs Firezone.**
+
+- [Erlang/OTP](https://www.erlang.org)
+- [Elixir](https://elixir-lang.org)
+- [NodeJS](https://nodejs.org)
+
+# Steps
+
+From your terminal, run these steps to build Firezone:
+
+```bash
+git clone https://github.com/firezone/firezone
+cd firezone
+mix local.rebar --force
+mix local.hex --force
+MIX_ENV=prod mix deps.get
+MIX_ENV=prod mix release
+```
+
+After the release build finishes, you should have a shiny new Firezone instance at
+`<CURRENT_DIR>/_build/dev/rel/firezone`. In the `bin` folder, the `firezone` binary
+can be used to start up Firezone. If you run it without any arguments you should see
+a list of available commands like this:
+
+```bash
+Usage: firezone COMMAND [ARGS]
+
+The known commands are:
+
+    start          Starts the system
+    start_iex      Starts the system with IEx attached
+    daemon         Starts the system as a daemon
+    daemon_iex     Starts the system as a daemon with IEx attached
+    eval "EXPR"    Executes the given expression on a new, non-booted system
+    rpc "EXPR"     Executes the given expression remotely on the running system
+    remote         Connects to the running system via a remote shell
+    restart        Restarts the running system via a remote command
+    stop           Stops the running system via a remote command
+    pid            Prints the operating system PID of the running system via a remote command
+    version        Prints the release name and version to be booted
+```
+Most deployment-related configuration is handled with environment variables. You'll probably want to at least set variables related to your reverse proxy and database. See the [ENV var reference](/reference/env-vars/) for an exhaustive list.
+
+Now all you need are the database and reverse proxy that you've previously set up.
+Once that's done, you can use `firezone start` to start Firezone and run
+`create-or-reset-admin` (in the same `bin` dir) to create the admin user and use
+it to log into Firezone from a web browser to start setting up your brand new
+custom instance that you built by hand with a little bit of elbow grease :)
+
+:::info
+As mentioned at the top, it's recommended to use some sort of service management
+to start and stop Firezone easily without having to manually do it using the
+`firezone` binary directly. But the choice is yours, since you're in control!
+:::

docs/docs/deploy/advanced/reverse-proxy.mdx

@@ -68,7 +68,7 @@ Read more about the configuration options
   enforce [secure cookies](
   https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#restrict_access_to_cookies).
 * Firezone requires the use of WebSockets to establish realtime connections. We
-  recommended following your proxy's specific documentation for supporting
+  recommend following your proxy's specific documentation for supporting
   WebSockets as each proxy varies. In general, your proxy needs to be able to
   proxy HTTP 1.1 connections, and the Firezone web app expects the following
   headers to be set: