Make the OPT recomendation clearer

AFAIK OTP releases are the recomended way of installing, but

  * People seem unaware of that and use from source installations because they use the guide with the name of their distro
  * People don't know what OTP releases are or what it means

I added a warning on all installation-from-source guides and added the same explanation on the two OTP pages (the miigration to OTP and installing OTP)

docs/installation/alpine_linux_en.md

@@ -1,4 +1,7 @@
 # Installing on Alpine Linux
+
+{! backend/installation/otp_vs_from_source_source.include !}
+
 ## Installation
 
 This guide is a step-by-step installation guide for Alpine Linux. The instructions were verified against Alpine v3.10 standard image. You might miss additional dependencies if you use `netboot` instead.

docs/installation/arch_linux_en.md

@@ -1,4 +1,7 @@
 # Installing on Arch Linux
+
+{! backend/installation/otp_vs_from_source_source.include !}
+
 ## Installation
 
 This guide will assume that you have administrative rights, either as root or a user with [sudo permissions](https://wiki.archlinux.org/index.php/Sudo). If you want to run this guide with root, ignore the `sudo` at the beginning of the lines, unless it calls a user like `sudo -Hu pleroma`; in this case, use `su <username> -s $SHELL -c 'command'` instead.

docs/installation/debian_based_en.md

@@ -1,4 +1,7 @@
 # Installing on Debian Based Distributions
+
+{! backend/installation/otp_vs_from_source_source.include !}
+
 ## Installation
 
 This guide will assume you are on Debian 11 (“bullseye”) or later. This guide should also work with Ubuntu 18.04 (“Bionic Beaver”) and later. It also assumes that you have administrative rights, either as root or a user with [sudo permissions](https://www.digitalocean.com/community/tutorials/how-to-add-delete-and-grant-sudo-privileges-to-users-on-a-debian-vps). If you want to run this guide with root, ignore the `sudo` at the beginning of the lines, unless it calls a user like `sudo -Hu pleroma`; in this case, use `su <username> -s $SHELL -c 'command'` instead.

docs/installation/gentoo_en.md

@@ -1,4 +1,7 @@
 # Installing on Gentoo GNU/Linux
+
+{! backend/installation/otp_vs_from_source_source.include !}
+
 ## Installation
 
 This guide will assume that you have administrative rights, either as root or a user with [sudo permissions](https://wiki.gentoo.org/wiki/Sudo). Lines that begin with `#` indicate that they should be run as the superuser. Lines using `$` should be run as the indicated user, e.g. `pleroma$` should be run as the `pleroma` user.

docs/installation/migrating_from_source_otp_en.md

@@ -1,7 +1,8 @@
 # Switching a from-source install to OTP releases
 
-## What are OTP releases?
+{! backend/installation/otp_vs_from_source.include !}
-OTP releases are as close as you can get to binary releases with Erlang/Elixir. The release is self-contained, and provides everything needed to boot it, it is easily administered via the provided shell script to open up a remote console, start/stop/restart the release, start in the background, send remote commands, and more.
+
+In this guide we cover how you can migrate from a from source installation to one using OTP releases.
 
 ## Pre-requisites
 You will be running commands as root. If you aren't root already, please elevate your priviledges by executing `sudo su`/`su`.

docs/installation/otp_en.md

@@ -1,5 +1,9 @@
 # Installing on Linux using OTP releases
 
+{! backend/installation/otp_vs_from_source.include !}
+
+This guide covers a installation using an OTP release. To install Pleroma from source, please check out the corresponding guide for your distro.
+
 ## Pre-requisites
 * A machine running Linux with GNU (e.g. Debian, Ubuntu) or musl (e.g. Alpine) libc and `x86_64`, `aarch64` or `armv7l` CPU, you have root access to. If you are not sure if it's compatible see [Detecting flavour section](#detecting-flavour) below
 * A (sub)domain pointed to the machine

docs/installation/otp_vs_from_source.include

@@ -0,0 +1,3 @@
+## OTP releases vs from-source installations
+
+There are two ways to install Pleroma. You can use OTP releases or do a from-source installation. OTP releases are as close as you can get to binary releases with Erlang/Elixir. The release is self-contained, and provides everything needed to boot it, it is easily administered via the provided shell script to open up a remote console, start/stop/restart the release, start in the background, send remote commands, and more. With from source installations you install Pleroma from source, meaning you have to install certain dependencies like Erlang+Elixir and compile Pleroma yourself.

docs/installation/otp_vs_from_source_source.include

@@ -0,0 +1,3 @@
+{! backend/installation/otp_vs_from_source.include !}
+
+This guide covers a from-source installation. To install using OTP releases, please check out [the OTP guide](./otp_en.md).