Customise example docs build to use sunpy theme and other minor tweaks

[Cadair]

Describe the feature

This is not a request to make docs/conf.py fully templated, but we should at least make it so that a new package using the template builds with the sunpy sphinx theme.

Proposed solution

No response

[Cadair]

Also removing the index and maybe some of the home page stuff? Actually now I think about it could we make it so that we don't template index.rst and some docs stuff on an ongoing basis but can do on a first run?!

[Cadair]

partially fixed by #136