Environment.md: reset_ps1 function now with whoami

After loading the pyenv, my ps1 loses all user info
instead of:
[masnes@localhost ~]$
I have:
(py3) ~$
after reset_ps1:
~$
This improves things a little by changing it to:
masnes ~$

Adding hostname may also be desireable, but I found that hostname
is too long (localhost.localdomain) in the vm. Hostname -s would
fix this, but I don't trust it.