Remove slave-master terminology from howto

http://wmj5kiic7b6kjplpbvwadnht2nh2qnkbnqtcv3dyvpqtz7ssbssftxid.onion/about.privacy/messengers-on-tails-os/-/wikis/HowTo#signal

Signal Desktop is a slave client for using Signal with an already registered account. Accounts can be registered only with a master client, either an Android or iOS device or using signal-cli as master.

Could we rewrite this to not use this language?