Update README

The README should have links to the latest source release and PyPi.
>  assume that people know Python. The current wording is fine: If you know Python, you will know what that sentence means.

I'm sure many intermediate-level Python programmers don't know exactly when `__del__()` is called in their interpreter, let alone in other interpreters.
And the good thing is: they don't have to, as long as they do the Pythonic thing (use `close()` or a context manager).

People who know exactly how and when `__del__()` is called, won't really care what's written in the README. But we shouldn't teach newbies who don't know bad style.

But it really doesn't matter how much people know or don't know. The Python manual "strongly recommends" to close files, that should be reason enough.

> No need to be hypocritical.

I don't see how this is hypocritical.

In all parts of the documentation (and to some minor extent in the code itself), I try to encourage good and idiomatic programming style.
That's also what I'm trying to do here.
It may be nit-picky, but I don't think it's hypocritical.

> Practicality beats purity.

Sure, but we are on a pedagogical mission here, we shouldn't teach sloppiness, laziness and bad style.

And, since you brought up the Zen: Explicit is better than implicit.