Documentation typo

[gnthibault]

Dear all,

I am discovering this excellent software, and its good documentation (a really cool source of informations for me).

As there does not seem to be much opensource tool to analyse astro image quality on linux (like ccd inspector), I was impressed by the quality of this software.

I am definitely interested in testing it and using it. at some point, I also would like to implement proper python binding with Pybind11, if I have time.

Anyway, for now, I just wanted to report what I think is a small typo in the documentation:
https://psfex.readthedocs.io/en/latest/Installing.html

I think on ubuntu it is

sudo apt-get install psfex

instead of

apt-get psfex

It is not much, but I wanted to use this issue section to thank you for all the work