Improve renewal instructions in the instruction generator

[ohemorange]

These changes are done to match our updated cli ux, our updated docs instructions, and feedback from the CISPA Usable Security group.

pip apache (cron not included, no certonly)

pip other (cron not included, certonly)

snapd apache (cron included, no certonly)

snapd other (cron included, certonly)

This PR does not include the Windows instructions, which are hard-coded on their own in windows.html.

[alexzorin]

Why are we not showing pip users how to do a --dry-run in addition to setting up the cronjob?

Approving because this problem is in master already and I don't mind if we address it in a follow-up PR.

This otherwise LGTM.

[ohemorange]

Follow-up PR is here: #718