update documentation about SECRET_KEY in bepasty-server/src/bepasty/config.py

[IeP4nieF]

At the moment the documentation is:

#: server secret key needed for safe session cookies.
#: you must set a very long, very random, very secret string here,
#: otherwise bepasty will not work (and crash when trying to log in)!

What is the meaning of "very long" in this context? For a developer it might be obvious, but for a first time installation you don't know how many characters you should use. Is 32 very long or is 2^10 very long? Or even more?

Please give an example for the length of this string.

[ThomasWaldmann]

This is the official docs for that:

https://flask.palletsprojects.com/en/2.3.x/config/#SECRET_KEY

So, rather 20-100 than 1024+.