[user] prioritize 'user' directory if it exists (without needing a portable build) + docs (#338)

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Reviewed-on: #338
Reviewed-by: crueter <crueter@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

docs/User.md

@@ -0,0 +1,11 @@
+# User configuration
+
+## Configuration directories
+
+Eden will store configuration in the following directories:
+
+- **Windows**: `%AppData%\Roaming`.
+- **Android**: Data is stored internally.
+- **Linux, macOS, FreeBSD, Solaris, OpenBSD**: `$XDG_DATA_HOME`, `$XDG_CACHE_HOME`, `$XDG_CONFIG_HOME`.
+
+If a `user` directory is present in the current working directory, that will override all global configuration directories and the emulator will use that instead.