sanity_check: Improve output for manual installation.
sanity_check: Improve output for manual installation.

We should still display the `source` advice when not in Vagrant or a
Droplet, since that's an important hint for anyone using local
installation on Linux.

We move the "If you are using Vagrant..." text a bit after to
highlight things nicely for folks who are running tools outside
Vagrant.

Also tighten text to avoid line-wrapping on an 80 character console.

kou/zulip,punchagan/zulip,hackerkid/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,rht/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,zulip/zulip,zulip/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,rht/zulip,punchagan/zulip,andersk/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,kou/zulip,andersk/zulip,kou/zulip,rht/zulip,andersk/zulip,zulip/zulip,hackerkid/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,rht/zulip