Add support for Lua input (#1810)

pkg/yqlib/doc/usage/lua.md

@@ -1,5 +1,33 @@
 
-## Basic example
+## Basic input example
+Given a sample.lua file of:
+```lua
+return {
+	["country"] = "Australia"; -- this place
+	["cities"] = {
+		"Sydney",
+		"Melbourne",
+		"Brisbane",
+		"Perth",
+	};
+};
+
+```
+then
+```bash
+yq -oy '.' sample.lua
+```
+will output
+```yaml
+country: Australia
+cities:
+  - Sydney
+  - Melbourne
+  - Brisbane
+  - Perth
+```
+
+## Basic output example
 Given a sample.yml file of:
 ```yaml
 ---