Don't show the password plainly in `addrb -h`

[doronbehar]

Although you require this information as an environment variable, it's not considered good practice to print it like that.

addrb/addrb.go

Line 47 in 785d726

os.Getenv("CARDDAV_PASSWORD"),

[mrusme]

What's the different between:

export CARDDAV_PASSWORD='abc123'
addrb -h

and

export CARDDAV_PASSWORD='abc123'
echo $CARDDAV_PASSWORD

?