Rewrite the README to be clear and succinct

This modernises the project's README to match the current state of the
project (ie dropping tools we should look at), tidies up the prose to be
more succinct, and splits out contribution docs to CONTRIBUTING.md.

The contributor docs have been streamlined to point to the `make`
commands where possible.  I've also added a section from #245 on where
the project is going.  It's a long piece of work so my hope is this sets
expectations without making the maintainers feel bad when folks raise a
PR for defunct or soon-to-be-removed code paths.

Author: ghickman

CONTRIBUTING.md

@@ -9,7 +9,7 @@ The [Low-hanging fruit tag](https://github.com/classy-python/ccbv/issues?q=is%3A
 > CCBV runs as a Django site, pulling data from a database.
 > This made it very fast to get up and running, and easy to maintain for the Django-using developers, but it has been a thorn in the side of the project for years.
 > The dataset is entirely fixed.
-> Any changes to the GCBVs only happen in a release of Django.
+> Any changes to Django's generic class based views (GCBVs) only happen when Django makes a new release.
 > We do not need to dynamically construct templates from the data on every request.
 > We can write out some HTML and never touch it again (unless we feel like changing the site's styles!)
 > The inspection code is tightly coupled to Django's GCBVs.
@@ -40,4 +40,3 @@ Run `make compile` and appropriate txt file will be updated.
 
 ## Testing
 Run `make test` to run the full test suite with coverage.
-

README.md

@@ -1,7 +1,7 @@
 # [Classy Class Based Views](https://ccbv.co.uk)
 
 Django's Generic class-based views provide a lot of common functionality to users.
-However, they are made up of up to nine, at the time of writing, parent classes or mixins.
+However, they are made up of up to twelve parent classes or mixins, at the time of writing.
 Knowing what functionality comes from which parent class/mixin is a tricky proposition.
 
 CCBV provides a breakdown of each view's inheritance hierarchy, methods, and attributes.