Simplify Wagtail docs section titles

- Avoid additional 'Wagtail' names in the docs titles (inc. contributing)

.github/CONTRIBUTING.md

@@ -1,4 +1,4 @@
-# Contributing to Wagtail
+# Contributing
 
 Thank you for considering to help Wagtail.
 

docs/advanced_topics/index.md

@@ -1,4 +1,4 @@
-# Advanced topics
+# Advanced
 
 ```{toctree}
 ---

docs/contributing/index.md

@@ -1,4 +1,4 @@
-# Contributing to Wagtail
+# Contributing
 
 Thank you for your interest in improving Wagtail!
 

docs/editor_manual/index.md

@@ -1,3 +1,3 @@
-# Using Wagtail: an Editor's guide
+# Editor's guide
 
 Wagtail’s Editor Guide now has its own website: [guide.wagtail.org](https://guide.wagtail.org/). This guide is written for the users of a Wagtail-powered site. That is, the content editors, moderators and administrators who will be running things on a day-to-day basis.

docs/extending/index.md

@@ -1,4 +1,4 @@
-# Extending Wagtail
+# Extending
 
 The Wagtail admin interface is a suite of Django apps, and so the familiar concepts from Django development - views, templates, URL routes and so on - can be used to add new functionality to Wagtail. Numerous [third-party packages](https://wagtail.org/packages/) can be installed to extend Wagtail's capabilities.