Document `OpenBSDBCrypt` password handling

[Marcono1234]

Previously the behavior was not explicitly documented, and it might not have been obvious that passwords longer than 72 bytes will be truncated.

[Marcono1234]

Maybe it would also be good to apply this to https://github.com/bcgit/bc-csharp, but I am not familiar with C#. So if possible, could you do that please?

[Marcono1234]

Thanks for merging @dghgit!

Regarding https://github.com/bcgit/bc-csharp, could you please adjust the documentation there as well (I am not familiar enough with C#)? Or would you prefer if I created a GitHub issue there so that this task it as least tracked?

[dghgit]

I updated C# as well. You should see the update appear on github shortly.