Update security information

[dichotommy]

The keys + authentication sections can use an update. Specify that master key can be a string of any length.

Tools for generating master keys:

• 1password
• shasum
• uuidgen
• https://randomkeygen.com/
• openssl rand

Some cybersecurity basics:

• Recommended number of bits of entropy (256 minimum?)

Related to #662

[bidoubiwa]

Maybe avoid 1password as it is a closed-source and not a free tool. Everything else tip top