Added Composer installation tip
feature #4099 Composer installation verbosity tip (dannykopping)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4099).

Discussion
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Composer installation verbosity tip

Added installation verbosity tip, for users with slow internet connections.

With love from slow South Africa :earth_africa:

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f8d69d4 Added Composer installation tip