1st line of the math.perm docstring doesn't mention a default value for k

[skirpichev]

Here is an example how this looks in the IDLE:

While full docstring and the sphinx docs looks fine, the first line doesn't describe the function signature correctly.

Originally posted by @skirpichev in #89381 (comment)

[rhettinger]

I think this is unimportant. There is only a limited amount of information that can be squeezed into the first line. The default k=None is the least important case and its functionality is duplicated by factorial.

So, I'll mark this one as "don't worry about it".

[skirpichev]

There is only a limited amount of information that can be squeezed into the first line.

Sure, I realize that.

The default k=None is the least important case

The point is that it's not an obvious default value, as it was noted by @serhiy-storchaka in #81359. IMHO, even less obvious than the log case, where that was an issue.