add optional dependencies to PyPI description

Description

With the change to lalpulsar ephemerides, I think we need to make this clear to users. The lalinference and test options were also difficult to discover so far.

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

@duncanmmacleod @leo-singer @karl-wette @adam-mercer please have a look at the wording and maybe syntax too.