Fix Jupyter Lite serve instruction

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

Without this change, the documentation tag won't work when build locally.

Fixes # (issue)

Type of change

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• Bug fix
• New feature
• Requires documentation updates

Testing

Please describe the test(s) that you added and ran to verify your changes.

Checklist

• I have read the contribution guide recently

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.30%. Comparing base (10e0d5d) to head (6c846eb).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #654   +/-   ##
=======================================
  Coverage   79.30%   79.30%           
=======================================
  Files           9        9           
  Lines        3876     3876           
=======================================
  Hits         3074     3074           
  Misses        802      802           

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[mcbarton]

This PR has been changed to match the documentation change made in xeus-cpp, so should be ready to go.