hterm/nassh: improve some descriptions and translation tips
hterm/nassh: improve some descriptions and translation tips

Largely based on feedback/questions from translators.

Change-Id: I436bff593ed9bef0efe30339c4d87a7f783a98fa
Reviewed-on: https://chromium-review.googlesource.com/c/apps/libapps/+/2241136
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Joel Hockey <9ecfc52dc2ffef73afac73f3495f294aeddf1231@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm