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/We.yml

@@ -0,0 +1,11 @@
+extends: existence
+message: "Try to avoid using first-person plural like '%s'."
+link: 'https://developers.google.com/style/pronouns#personal-pronouns'
+level: warning
+ignorecase: true
+tokens:
+  - we
+  - we'(?:ve|re)
+  - ours?
+  - us
+  - let's