Add information about steps required before importing your migrated data.

[kwacky1]

Why:

If you land on this page from a search, there is no indication that prior steps are required.

What's being changed:

A small preamble is added before the process that mentions and links to the previous steps

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[felicitymay]

Thanks for raising this PR. It's a good call to add this extra context to the start of this procedure for people who arrive from a search ✨

There's one change needed to bring this into line with our localization guidelines. Otherwise this looks like a great change.

You can see your changes on staging here: https://docs-4007--kwacky1-migration-c.herokuapp.com/en/enterprise-server@3.0/admin/user-management/migrating-data-to-your-enterprise.

[sartgoo]

team-review-requested:[TEAMNAME4007[USERNAME]

[felicitymay]

Thanks. This looks ready to merge once the repository is unfrozen (should be today).