Prepare CLI for move into mainline

packages/cli/docs/src/plugin/interface/os.md

@@ -0,0 +1,11 @@
+# OS Functions
+
+> you can use OS functions to get some system information
+
+### current_platform() -> string ("windows" | "macos" | "linux")
+
+This function can help you get system & platform type:
+
+```lua
+local platform = plugin.os.current_platform()
+```