Add agreed word usage guidance for 64-bit architecture

[julian-cable]

Add the following guidance as approved by the Word Nerds group:
https://docs.google.com/document/d/1jMxBFk2FiYKl9S71bnsG3hnR_8wxd5hOM7JOtwG-lSM/edit

[julian-cable]

Additional guidance to add for the next release.