[Integrated] RFR: git-pr: friendly help message when missing action

[Erik Helin]

Changeset: a57c1319
Author:    Erik Helin <ehelin at openjdk.org>
Date:      2020-02-06 11:12:29 +0000
URL:       https://git.openjdk.java.net/skara/commit/a57c1319

git-pr: friendly help message when missing action

Reviewed-by: rwestberg

! cli/src/main/java/org/openjdk/skara/cli/GitPr.java