Use Package Control to install "QuickRulers".
Create a key binding
for the quick_rulers command,
and use it.
Features live preview and restore-on-cancel.
Here are two example bindings:
[
{ "keys": ["alt+r"], "command": "quick_rulers" },
{ "keys": ["alt+shift+r"], "command": "quick_rulers",
"args": {"show_current": false} }
]