Add a note on issues with special characters for pypi deployments passwords

[iriberri]

This issue about PyPI deployments not working when "special" chars in password is affecting several people. In one of these reports we got a request to add this to the Pypi deployment documentation (https://docs.travis-ci.com/user/deployment/pypi/), and I think it's a great idea as this can help users detect the problem.

We already have a very detailed section there on how to authenticate with pypi, so I believe adding a note for this would make a nice addition.

[stale]

Thanks for contributing to this issue. As it has been 90 days since the last activity, we are automatically closing the issue. This is often because the request was already solved in some way and it just wasn't updated or it's no longer applicable. If that's not the case, please do feel free to either reopen this issue or open a new one. We'll gladly take a look again! You can read more here: https://blog.travis-ci.com/2018-03-09-closing-old-issues