Added cffi/* module for third-party advanced modules

resources/custom_modules/cffi_example/README.md

@@ -0,0 +1,35 @@
+# C FFI module
+
+A C FFI module is a dynamic library that exposes standard C functions and
+constants, that Waybar can load and execute to create custom advanced widgets.
+
+Most language can implement the required functions and constants (C, C++, Rust,
+Go, Python, ...), meaning you can develop custom modules using your language of
+choice, as long as there's GTK bindings.
+
+# Usage
+
+## Building this module
+
+```bash
+meson setup build
+meson compile -C build
+```
+
+## Load the module
+
+Edit your waybar config:
+```json
+{
+	// ...
+	"modules-center": [
+		// ...
+		"cffi/c_example"
+	],
+	// ...
+	"cffi/c_example": {
+		// Path to the compiled dynamic library file
+		"module_path": "resources/custom_modules/cffi_example/build/wb_cffi_example.so"
+	}
+}
+```