Add Re-indenting Your Code as a vim til.

vim/reindenting-your-code.md

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+# Re-indenting Your Code
+
+If you have pasted some poorly formatted code or you've written a portion
+of code in a way that mangled the indentation, you can quickly re-indent
+that code for you. Or at least do its best to try and indent it correctly.
+
+Make a visual selection of the code that you want to re-indent and then
+hit `=`.
+
+For instance, this ruby code
+
+```ruby
+if this_thing
+p something
+else
+p nothing
+end
+```
+
+will be indented by Vim as
+
+```ruby
+if this_thing
+  p something
+else
+  p nothing
+end
+```
+
+See `:h =` for more details on how vim decides what formatting and
+indenting it will do.
+
+h/t [Chris Erin](https://twitter.com/MCNormalMode)