Add retext-case-police to list of plugins

Closes GH-78.

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

doc/plugins.md

@@ -24,6 +24,8 @@ The list of plugins:
 
 *   [`retext-assuming`](https://github.com/davidhund/retext-assuming)
     — check for unhelpful phrases such as `just`, `simply`, `obviously`
+*   [`retext-case-police`](https://github.com/JulianCataldo/retext-case-police)
+    — check for popular names casing (`github` → `GitHub`)
 *   [`retext-cliches`](https://github.com/dunckr/retext-cliches)
     — check phrases for cliches
 *   [`retext-contractions`](https://github.com/retextjs/retext-contractions)
@@ -73,7 +75,7 @@ The list of plugins:
 *   [`retext-syntax-mentions`](https://github.com/retextjs/retext-syntax-mentions)
     — classify `@mentions` as syntax
 *   [`retext-syntax-urls`](https://github.com/retextjs/retext-syntax-urls)
-    — Classify url-like values (example.com, example.md, etc) as syntax
+    — classify url-like values (example.com, example.md, etc) as syntax
 *   [`retext-usage`](https://github.com/admhlt/retext-usage)
     — check incorrect English usage
 *   [`retext-quotes`](https://github.com/retextjs/retext-quotes)