Update CONTRIBUTING.md and add recommended extensions

Signed-off-by: Eddie Carswell <[email protected]>

.vscode/extensions.json

@@ -0,0 +1,3 @@
+{
+  "recommendations": ["timonwong.shellcheck", "foxundermoon.shell-format"]
+}

docs/CONTRIBUTING.md

@@ -9,15 +9,27 @@ For bug reports and feature requests, open an issue and provide any relevant
 details there. Questions are not well suited to issue format, and may be better
 addressed by asking instead on [Gitter].
 
+## Code contributions
+
 For pull requests, features and bug fixes should be submitted to the `dev`
 branch. Bug fixes will also get pushed to `master` or the relevant release
-branch when needed. Code submissions should be [lint] free, and follow best
-practices where possible.
+branch when needed. Code submissions should be lint free and follow best
+practices where possible. We use [shellcheck] and [shfmt] for this purpose. If
+you're using VSCode, it will recommend them when you open this repo.
+
+The code generally follows Google's Bash style [guide], with notable exceptions:
+
+- Indent with four spaces, no tabs. The `.editorconfig` file helps with this.
+- Pipeline and compounds (e.g. `|` or `&&`) end a line instead of beginning it.
+- Variables are brace delimited (`${var}`) only when needed, but always quoted.
+- Function namespacing is done with `.` instead of `::` (e.g. `module.func()`).
 
 By making contributions to this project you agree to follow the conditions laid
 out in the [Developer Certificate of Origin][cert].
 
 [issue]: https://github.com/AfroThundr3007730/syncrepo/issues/new
 [gitter]: https://matrix.to/#/#syncrepo:gitter.im
-[lint]: https://github.com/koalaman/shellcheck
+[shellcheck]: https://github.com/koalaman/shellcheck
+[shfmt]: https://github.com/mvdan/sh
+[guide]: https://github.com/google/styleguide/blob/gh-pages/shellguide.md
 [cert]: https://developercertificate.org/