Add Listing Files In IEx as an elixir til

elixir/listing-files-in-iex.md

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+# Listing Files In IEx
+
+When you start an IEx session, you do so in the context of some directory --
+the current working directory. This context can be important if you need to
+do something like import a file. In fact, you may want to know what files
+are available in the current working directory.
+
+You can list them all out within IEx using `ls/0`.
+
+```elixir
+iex(1)> ls()
+           .git     .gitignore      README.md         _build         assets         config
+           deps            lib        mix.exs       mix.lock           priv           test
+            tmp
+```
+
+You can also list the contents of some other specific directory by naming it
+when invoking `ls/1`.
+
+See `h()` within IEx for more details.