iex: add page (#4658)

pages/common/iex.md

@@ -0,0 +1,16 @@
+# iex
+
+> IEx is the interactive shell for Elixir.
+> More information: <https://hexdocs.pm/iex>.
+
+- Start an interactive session:
+
+`iex`
+
+- Start a session that remembers history:
+
+`iex --erl "-kernel shell_history enabled"`
+
+- Start and load Mix project files:
+
+`iex -S mix`