Update quick action help text

Problem to solve

The hyperlink for quick actions does not create a clear enough call-to-action. It also requires a user to go to a different page to understand how to initiate them.

Proposal

Add the keyboard action for / into the help text.

app/assets/javascripts/vue_shared/components/markdown/toolbar.vue

Current

Proposed

References

Idea from @jeldergl in Slack thread: