elm: add page (#2365)

pages/common/elm.md

@@ -0,0 +1,15 @@
+# elm
+
+> Run and manage programs in Elm programming language.
+
+- Start an interactive Elm shell (REPL):
+
+`elm --repl`
+
+- Initialize an empty Elm project:
+
+`elm --init`
+
+- Compile the current project and serve it via the local web server:
+
+`elm --reactor`