Enable vale for prose linting (#3)

* Enable vale in CI

* Add vale config

* Tweak vale

* Update config

* Update .gitignore

* Switch back

* Rename CI

* Add badges

* Tidy up CI

* Change image

* Configure vale

* Delint

* Update README

.github/styles/Google/FirstPerson.yml

@@ -0,0 +1,13 @@
+extends: existence
+message: "Avoid first-person pronouns such as '%s'."
+link: 'https://developers.google.com/style/pronouns#personal-pronouns'
+ignorecase: true
+level: warning
+nonword: true
+tokens:
+  - (?:^|\s)I\s
+  - (?:^|\s)I,\s
+  - \bI'm\b
+  - \bme\b
+  - \bmy\b
+  - \bmine\b