Add documentation or typing annotatations

[ShadowJonathan]

Currently, when surveying this library for its intended usage in another application, i found out it does not annotate any types of its sort, tracing all the way back to a cryptic execute_command function reference, with which i could not (reliably) found out what kind of type translation takes place back to python typing.

I could also not find any supplementary documentation stating all/any of this, which does not help at all.

Please add some rudimentary documentation detailing return types and some basic overview of the library, or type annotations tho implicitly signal to IDEs or static analysis tools what type is returned when executing certain functions.

[IlyaSkriblovsky]

Yeah, docs for this library leaves much space for improvement :(

I'm currently integrating mypy checking into my work project where we use this txredisapi library, so I will eventually face the same issue of type annotations absence.

I will try to find time to write down some details and add type hints for txredisapi.