Address remaining comments for onboarding tour

Created by: attfarhan

A few comments were left unaddressed in the onboarding tour. This PR resolves them:

• https://github.com/sourcegraph/sourcegraph/pull/12972/files/732db55c9694a02c41cb7abda112b250fc867d35#diff-1fc920dc0dce4d3ceb4d02ad4940f8cb
• https://github.com/sourcegraph/sourcegraph/pull/12972/files/732db55c9694a02c41cb7abda112b250fc867d35#diff-4fff7ba9a0e302afd10b8781da901327
• https://github.com/sourcegraph/sourcegraph/pull/12972/files/732db55c9694a02c41cb7abda112b250fc867d35#r472364343