Add needed comment to user class & change "GITHUB USERNAME"
Add needed comment to user class & change "GITHUB USERNAME"

The comment is needed, without it the PR will fail the linter.  Also,
it's the SSH username (which is the FIRSTNAMELASTNAME), not the GitHub
username.

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs