lua: add page (#1381)

pages/common/lua.md

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+# lua
+
+> A powerful, light-weight embeddable programming language.
+
+- Start an interactive Lua shell:
+
+`lua`
+
+- Execute a Lua script:
+
+`lua {{script_name.lua}} {{--optional-argument}}`
+
+- Execute a Lua expression:
+
+`lua -e '{{print( "Hello World" )}}`