Updated Readme and added Minimum password length and strength check

[danieltayal07]

added 2 features:

Passwords are now always generated with a minimum length.

Password strength is checked, and user is warned if the generated password does not meet the criteria.

Also expanded user guide and contributor instructions in README.md

hope this is useful, if yes please consider!

Thanks!

[SpreadSheets600]

@danieltayal07 update according to suggestion made in #13