feat(ci): mirror docs repo (#1131)

Adds a github action to use https://github.com/ingydotnet/git-subrepo to push to the docs repo whenever the docs folder updates.

README.md

@@ -1,3 +1,4 @@
+
 # Aztec Protocol Documentation
 
 You can view the latest successful build here. https://docs.aztec.network
@@ -42,4 +43,4 @@ This command starts a local development server and opens up a browser window. Mo
 $ yarn build
 ```
 
-This command generates static content into the `build` directory and can be served using any static contents hosting service.
+This command generates static content into the `build` directory and can be served using any static contents hosting service.

src/css/custom.css

@@ -64,4 +64,4 @@
 @font-face {
   font-family: 'Plain-Regular';
   src: url('../../static/font/Plain-Regular.otf');
-}
+}