don't waste hard drive space with Windows-only QT submodule

Building-for-Linux.md

@@ -28,9 +28,18 @@ crew install xorg_nouveau_driver
 ```
 
 ## Checkout Dolphin
-1. `git clone --recursive https://github.com/dolphin-emu/dolphin`
+1. `git clone https://github.com/dolphin-emu/dolphin`
 2. `cd dolphin`
 
+## Add necessary submodules
+```bash
+git submodule update --init Externals/mGBA
+git submodule update --init Externals/spirv_cross
+git submodule update --init Externals/zlib-ng
+git submodule update --init Externals/libspng
+git pull --recurse-submodules
+```
+
 ## Building
 ### Global Build (if unsure, use this option)
 ```bash
@@ -82,10 +91,10 @@ cpack -G DEB
 ```
 
 ## Externally Managed Packages
-On some distributions of Linux, package maintainers provide unmodified builds of Dolphin. These are listed below:
+On some distributions of Linux, package maintainers provide unofficial, unmodified builds of Dolphin. These are listed below:
 
 - [Ubuntu](https://launchpad.net/~dolphin-emu/+archive/ubuntu/ppa) **as of the time of this writing, 16.04 and 18.04 only, for whatever reason - do NOT use this on anything newer**
-- [Debian](https://packages.debian.org/buster/games/dolphin-emu) **uses a highly outdated 6-year-old build**
+- [Debian](https://packages.debian.org/buster/games/dolphin-emu) (and, by extension, Ubuntu's apt repo) **uses a highly outdated 6-year-old build**
 - [Arch Linux](https://archlinux.org/packages/community/x86_64/dolphin-emu/)
 - [Fedora](https://packages.fedoraproject.org/pkgs/dolphin-emu/dolphin-emu/) **Follows the latest beta version but isn't quite always caught up with the most recent**
 - [OpenSUSE](https://software.opensuse.org/package/dolphin-emu)