Update warning message for --git-url and --zip-file lib install flags

[silvanocerza]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce?

Better feedback for the user.

• What is the current behavior?

Using --git-url or --zip-file flags with lib install command doesn't give great feedback to the user.

• What is the new behavior?

Using --git-url or --zip-file flags now tells the user to visit the documentation for more information.

• Does this PR introduce a breaking change?

No.

• Other information:

None.

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