Update coding documentation
Add conventions for shell shebangs.
@@ -485,6 +485,15 @@ To reformat a Markdown document in [TextMate][] every time you save it, please f
- Please only use [POSIX](https://en.wikipedia.org/wiki/POSIX) functionality.
+#### Shebang
+
+Every shell script must start with either of two shebangs:
+
+* `#!/bin/sh`
+* `#!/usr/bin/env <shell>`, where `<shell>` is an appropriate shell, e.g. `#!/usr/bin/env bash`
+
+Note that even if a shebang is added by a preprocessor macro or similar code generation tools, it must also be present in the templated file.
+
#### shfmt
We use [`shfmt`][] to format Shell files in the repository.
