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/Units.yml

@@ -0,0 +1,8 @@
+extends: existence
+message: "Put a nonbreaking space between the number and the unit in '%s'."
+link: "https://developers.google.com/style/units-of-measure"
+nonword: true
+level: error
+tokens:
+  - \b\d+(?:B|kB|MB|GB|TB)
+  - \b\d+(?:ns|ms|s|min|h|d)