Add style guide [ci skip]

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,13 +1,14 @@
 Before submitting your PR, check that you've:
 
-- [ ] Bumped the version number
-- [ ] Documented new APIs with [Haddock markup](https://www.haskell.org/haddock/doc/html/index.html)
-- [ ] Added [`@since` declarations](http://haskell-haddock.readthedocs.io/en/latest/markup.html#since) to the Haddock
+- [ ] Bumped the version number.
+- [ ] Documented new APIs with [Haddock markup](https://www.haskell.org/haddock/doc/html/index.html).
+- [ ] Added [`@since` declarations](http://haskell-haddock.readthedocs.io/en/latest/markup.html#since) to the Haddock.
+- [ ] Ran `stylish-haskell` and otherwise adhered to the [style guide](https://github.com/bitemyapp/esqueleto/blob/master/style-guide.yaml).
 
 After submitting your PR:
 
-- [ ] Update the Changelog.md file with a link to your PR
-- [ ] Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)
+- [ ] Update the Changelog.md file with a link to your PR.
+- [ ] Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts).
 
 <!---Thanks so much for contributing! :)
 

style-guide.md

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+# Style Guide
+
+- Please use `stylish-haskell` on the project to keep imports consistent and
+  clean. We have a custom [`.stylish-haskell.yaml`](.stylish-haskell.yaml) file.
+  You can run `stylish-haskell` from vim with `:%! stylish-haskell`.
+- Four space indent.
+- Prefer indentation over any other form of alignment.
+- If text goes off the screen due to four space indentation, factor out
+  functions and values into names to reduce indentation.