Update users_database.yml.example

[blakeashleyjr]

Using the command as currently provided results in an error:

Error: failed to read the password from the terminal: you must either use an interactive terminal or use the --password flag

We need to add a "--" between the command and the password to work now:

Usage:
authelia hash-password [flags] -- [password]

Examples:
authelia hash-password -- 'mypass'
authelia hash-password --sha512 -- 'mypass'
authelia hash-password --iterations=4 -- 'mypass'
authelia hash-password --memory=128 -- 'mypass'
authelia hash-password --parallelism=1 -- 'mypass' authelia hash-password --key-length=64 -- 'mypass'

Flags:
-c, --config strings configuration files to load (default [configuration.yml])
-h, --help help for hash-password
-i, --iterations int set the number of hashing iterations (default 3)
-k, --key-length int [argon2id] set the key length param (default 32)
-m, --memory int [argon2id] set the amount of memory param (in MB) (default 65536)
--no-confirm skip the password confirmation prompt
-p, --parallelism int [argon2id] set the parallelism param (default 4)
-l, --salt-length int set the auto-generated salt length (default 16)
-z, --sha512 use sha512 as the algorithm (changes iterations to 50000, change with -i)