Show help text when running nav command without arguments

[johannaengland]

Closes #2601.

[github-advanced-security]

You have successfully added a new SonarCloud configuration ``. As part of the setup process, we have scanned this repository and found no existing alerts. In the future, you will see all code scanning alerts on the repository Security tab.

[codecov]

Codecov Report

Merging #2603 (bc4c2cf) into 5.6.x (cbfc888) will not change coverage.
The diff coverage is n/a.

❗ Current head bc4c2cf differs from pull request most recent head ee2baf5. Consider uploading reports for the commit ee2baf5 to get more accurate results

@@           Coverage Diff           @@
##            5.6.x    #2603   +/-   ##
=======================================
  Coverage   53.89%   53.89%           
=======================================
  Files         558      558           
  Lines       40612    40612           
=======================================
  Hits        21887    21887           
  Misses      18725    18725           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[github-actions]

Test results

     12 files       12 suites   11m 52s ⏱️
3 222 tests 3 126 ✔️   96 💤 0 ❌
9 141 runs  8 853 ✔️ 288 💤 0 ❌

Results for commit ee2baf5.

♻️ This comment has been updated with latest results.

[lunkwill42]

👍

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[lunkwill42]

Still 👍