[docs] refactor: full rewrite, generalization + dedup (#488)

"docs but awesome"

Combines most of the stuff that was repeated thrice over verbatim into a
single common Build Instructions page, with additional caveats marked
elsewhere. Prettifies some stuff too because why not.

cc: @Lizzie @DraVee @MaranBr @SDK-Chan

Co-authored-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/488
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

docs/Caveats.md

@@ -0,0 +1,52 @@
+# Caveats
+
+## Arch Linux
+
+- httplib AUR package is broken. Set `httplib_FORCE_BUNDLED=ON` if you have it installed.
+- Eden is also available as an [AUR package](https://aur.archlinux.org/packages/eden-git). If you are unable to build, either use that or compare your process to the PKGBUILD.
+
+## Gentoo Linux
+
+Do not use the system sirit or xbyak packages.
+
+## macOS
+
+macOS is largely untested. Expect crashes, significant Vulkan issues, and other fun stuff.
+
+## Solaris
+
+Qt Widgets appears to be broken. For now, add `-DENABLE_QT=OFF` to your configure command. In the meantime, a Qt Quick frontend is in the works--check back later!
+
+This is needed for some dependencies that call cc directly (tz):
+
+```sh
+echo '#!/bin/sh' >cc
+echo 'gcc $@' >>cc
+chmod +x cc
+export PATH="$PATH:$PWD"
+```
+
+Default MESA is a bit outdated, the following environment variables should be set for a smoother experience:
+```sh
+export MESA_GL_VERSION_OVERRIDE=4.6
+export MESA_GLSL_VERSION_OVERRIDE=460
+export MESA_EXTENSION_MAX_YEAR=2025
+export MESA_DEBUG=1
+export MESA_VK_VERSION_OVERRIDE=1.3
+# Only if nvidia/intel drm drivers cause crashes, will severely hinder performance
+export LIBGL_ALWAYS_SOFTWARE=1
+```
+
+- Modify the generated ffmpeg.make (in build dir) if using multiple threads (base system `make` doesn't use `-j4`, so change for `gmake`).
+- If using OpenIndiana, due to a bug in SDL2's CMake configuration, audio driver defaults to SunOS `<sys/audioio.h>`, which does not exist on OpenIndiana. Using external or bundled SDL2 may solve this.
+- System OpenSSL generally does not work. Instead, use `-DYUZU_USE_BUNDLED_OPENSSL=ON` to use a bundled static OpenSSL, or build a system dependency from source.
+
+## OpenBSD
+
+After configuration, you may need to modify `externals/ffmpeg/CMakeFiles/ffmpeg-build/build.make` to use `-j$(nproc)` instead of just `-j`.
+
+## FreeBSD
+
+Eden is not currently available as a port on FreeBSD, though it is in the works. For now, the recommended method of usage is to compile it yourself.
+
+The available OpenSSL port (3.0.17) is out-of-date, and using a bundled static library instead is recommended; to do so, add `-DYUZU_USE_BUNDLED_OPENSSL=ON` to your CMake configure command.