add `py.typed` marker in order to be compatible with PEP 561

[amirsoroush]

Thanks for your great, well-written library.

Currently for people like me who have their Pylance's type checking mode set to strict, there is warning which says:

By adding a file named py.typed in the root of the project the problem will be gone:

From PEP 561:

Package maintainers who wish to support type checking of their code MUST add a marker file named py.typed to their package supporting typing.

I also think that this should be added in pyproject.toml file:

[tool.setuptools.package-data]
"aioclock" = ["py.typed"]

---

Also two tiny typos:

1. in line:

https://github.com/ManiMozaffar/aioclock/blob/main/aioclock/app.py#L229

it should be task actually, instead of group.

2. In the red note of the page https://manimozaffar.github.io/aioclock/latest/api/external_api/:

But this is a bit tricky and implicit because then your code gets ignored and "database" is preferred over the "database"

the second one should be codebase I guess.

[ManiMozaffar]

Thanks for the issue. I'll make the adjustment later. You can also do a PR if you wish to.