Reword note on missing CJK fonts

Use past tense as the fonts can be installed after the fact.
Add suggestion to install "Noto Sans CJK" and "Noto Serif CJK"
font families. ("Noto Serif CJK" is optional.)

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/dfefa601-c58d-c86c-953f-5e4454db9409@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>