Add a more self-contained pre-commit hook (#155)

The previous `pre-commit` hook declaration, using `language: 'script'`,
relied on `woke` already being installed on the user's path, which is a
somewhat awkward requirement compared to most other `pre-commit` hooks
which tend to be self-contained.  It also meant that it wasn't possible
to pin `woke` to a particular version on a per-repository basis using
something like `rev: v0.15.0`.

Using `language: 'golang'` instead means that `pre-commit` builds a
self-contained installation of `woke` for itself.  The only downside is
that the `go` binary on the user's path must be at least version 1.17,
which can be a bit annoying (for example, on Ubuntu 20.04 it requires
using something like the `go` snap rather than the .deb).  However, this
will become less of a problem over time.

In order to avoid a breaking change for people already using the old
approach, I added this as a new alternative hook, called
`woke-from-source`.

Add documentation for all this.

.pre-commit-hooks.yaml

@@ -3,3 +3,10 @@
   entry: scripts/pre-commit.sh
   language: 'script'
   description: "Runs `woke`"
+- id: woke-from-source
+  name: 'woke'
+  entry: woke
+  args: [--exit-1-on-failure]
+  # The 'go' binary on your path must be at least version 1.17.
+  language: 'golang'
+  description: "Runs `woke`, building it from source on demand"

docs/tools.md

@@ -4,3 +4,40 @@
 - [GitHub Action (reviewdog)](https://github.com/marketplace/actions/run-woke-with-reviewdog)
 - [VS Code Extension](https://marketplace.visualstudio.com/items?itemName=get-woke.vscode-woke)
 - [VIM Plugin](https://github.com/get-woke/vim-woke)
+
+## Pre-commit hook
+
+`woke` supports being run from a [pre-commit](https://pre-commit.com/) hook,
+allowing you to avoid accidentally committing uses of non-inclusive
+language.
+You have two alternative mechanisms for doing so.
+If you have arranged to install `woke` on your command search path (as well
+as anyone working on your repository), then add this configuration to your
+`.pre-commit-config.yaml`:
+
+```yaml
+-   repo: https://github.com/get-woke/woke
+    rev: ''  # pick a tag to point to
+    hooks:
+    -   woke
+```
+
+(Note that in this case the `rev` only controls the version of a wrapper
+script that is used, not the version of `woke` itself.)
+
+Alternatively, you can tell `pre-commit` to build `woke` from source,
+although this requires you and anyone working on your repository to have
+`go` on your command search path and for it to be at least version 1.17:
+
+```yaml
+-   repo: https://github.com/get-woke/woke
+    rev: ''  # pick a tag to point to
+    hooks:
+    -   woke-from-source
+```
+
+(In this case the `rev` controls the version of `woke` itself.)
+
+See the [pre-commit
+documentation](https://pre-commit.com/#pre-commit-configyaml---hooks) for
+how to customize this further.