Unix line endings

Closes #311

.editorconfig

@@ -1,4 +1,5 @@
 root = true
 
 [*]
+end_of_line = lf
 insert_final_newline = true

.github/CONTRIBUTING.md

@@ -0,0 +1,12 @@
+# Contributing
+
+## Formatting
+
+Contributors should configure their editor to use Unix line endings (`LF`).
+
+If you’re on a Windows machine and your editor is not correctly using Unix line endings,
+consider using [Git's `core.autocrlf`](https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration#_core_autocrlf) setting.
+On a Windows machine, set it to true — this converts LF endings into CRLF when you check out code:
+
+    $ git config core.autocrlf true
+