Update modrinth_gnu.md

Author: Axuras

docs/launcher/modrinth_gnu.md

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+# Modrinth App
+
+Modrinth App is an incredibly powerful launcher that makes managing your mods and modded instances much easier. It can do everything the official launcher can do, but allows for much more customization and ease of access. The official launcher has had several issues that have taken weeks to fix or are currently still not fixed, despite their severity. For modded and vanilla users alike, it is recommended to switch to Modrinth Launcher for an issue-less experience.
+
+This guide will explain the install process for Modrinth, as well as how we can use it for SkyClient. Please take the time after setting up to better learn your way around the launcher, as you may end up using it as your go-to launcher from now on!
+
+## How to Install (Linux)
+
+* Despite looking long, this is a very simple process and should only take a few minutes! This guide will also assume you are migrating from SkyClient, but steps will be largely the same, except for the migrating data section.