example: add README

example/README.md

@@ -0,0 +1,17 @@
+# Examples
+
+Standalone projects demonstrating the Ghostty library APIs.
+The directories starting with `c-` use the C API and the directories
+starting with `zig-` use the Zig API.
+
+Every example can be built and run using `zig build` and `zig build run`
+from within the respective example directory.
+Even the C API examples use the Zig build system (not the language) to
+build the project.
+
+## Running an Example
+
+```shell-session
+cd example/<dir>
+zig build run
+```