Remove refences to ARM OTP builds in install guide

Akkoma currently doesn't provide ARM OTP builds unlike Pleroma, so it's best to update the install guide to reflect that.

Ref: #424

docs/docs/installation/otp_en.md

@@ -5,7 +5,7 @@
 This guide covers a installation using an OTP release. To install Akkoma 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 machine running Linux with GNU (e.g. Debian, Ubuntu) or musl (e.g. Alpine) libc and an `x86_64` CPU you have root access to. If you are not sure if it's compatible see [Detecting flavour section](#detecting-flavour) below
 * For installing OTP releases on RedHat-based distros like Fedora and Centos Stream, please follow [this guide](./otp_redhat_en.md) instead.
 * A (sub)domain pointed to the machine