[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: #488
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

docs/README.md

@@ -0,0 +1,10 @@
+# Eden Build Documentation
+
+This contains documentation created by developers. This contains build instructions, guidelines, instructions/layouts for [cool stuff we made](CPM.md), and more.
+
+- **[General Build Instructions](Build.md)**
+- **[Development Guidelines](Development.md)**
+- **[Dependencies](Deps.md)**
+- **[CPM - CMake Package Manager](CPM.md)**
+- **[Platform-Specific Caveats](Caveats.md)**
+- **[User Directory Handling](User.md)**