merge AppImage builder into main repo with revised linux guide (#78)

Tested as working.

It is self-contained with no dependencies, uses relative paths, downloads what it needs on the fly, requires the main repo to already be cloned and built for native linux, so it doesn't need to be a separate repo.

- Copied the `build.sh` file and `assets` folder into a new `AppImageBuilder` folder on the torzu repo root.
- Created a `AppImage-build.sh` shortcut on the repo root that checks if an executable is already in `build/bin`. If it doesn't find one, it prompts the user to build a native version first. If it does find one:
    - enters the `AppImageBuilder` folder
    - runs the command `./build.sh ../build ./torzu.AppImage`, using the correct relative path to the build folder (if they followed the build instructions as directed)
    - moves the resulting `torzu.AppImage` executable back into the main `torzu` folder
    - returns back to the main folder and shows current directory contents
- Added relevant entries to `.gitignore`
- Added AppImage section to linux build guide, with some clarifying explanation for Flatpaks, and section separators

Co-authored-by: anon <anon@no.reply>
Reviewed-on: http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu/pulls/78
Co-authored-by: anon <anon@noreply.localhost>
Co-committed-by: anon <anon@noreply.localhost>

README.md

@@ -5,7 +5,7 @@ SPDX-License-Identifier: GPL-2.0-or-later
 
 <h1 align="center">
   <br>
-  <a href="http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu"><img src="./dist/yuzu.png" alt="torzu" width="200"></a>
+  <a href="http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu"><img src="https://notabug.org/litucks/torzu/raw/master/dist/yuzu.png" alt="torzu" width="200"></a>
   <br>
   <b>torzu</b>
   <br>
@@ -57,19 +57,25 @@ A secondary goal is the improvement of usability on low-end systems. This includ
 
 All development happens on [Dark Git](http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/). It's also where [our central repository](http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu) is hosted.
 
-To clone this git repository, you can use these commands given tor is installed and running:
+To clone this git repository, use these commands (assuming tor is installed as a service and running):
 
-    git -c http.proxy=socks5h://127.0.0.1:9050 clone --depth 1 http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu.git
-    cd torzu
-    git submodule update --init --recursive
+```bash
+git -c http.proxy=socks5h://127.0.0.1:9050 clone --depth 1 http://vub63vv26q6v27xzv2dtcd25xumubshogm67yrpaz2rculqxs7jlfqad.onion/torzu-emu/torzu.git
+cd torzu
+git submodule update --init --recursive
+```
 
 Alternatively, you can clone from the [NotABug mirror repository](https://notabug.org/litucks/torzu):
 
-    git clone https://notabug.org/litucks/torzu.git --depth 1 --recursive
+```bash
+git clone --depth 1 https://notabug.org/litucks/torzu.git
+cd torzu
+git submodule update --init --recursive
+```
 
 Note that above repository may be taken down any time. Do not rely on its existence in production. In case the NotABug mirror goes down, another mirror will be most likely be set up on Bitbucket.
 
-This project incorporates several commits from the [Suyu](https://suyu.dev) and [Sudachi](https://github.com/sudachi-emu/sudachi) forks (but cleaned up due to the typically mediocre code/commit quality from both projects) as well as changes listed in **Changes**.
+This project incorporates several commits from the [Suyu](https://suyu.dev) and [Sudachi](https://github.com/sudachi-emu/sudachi) forks, as well as changes listed in **Changes**.
 
 ## Move away from Codeberg
 
@@ -83,4 +89,4 @@ As requested by Codeberg staff, **I have removed the Codeberg mirror repository*
 
 ## License
 
-yuzu is licensed under the GPLv3 (or any later version). Refer to the [LICENSE.txt](./LICENSE.txt) file.
+torzu is licensed under the GPLv3 (or any later version). Refer to the [LICENSE.txt](./LICENSE.txt) file.