MT#62949 release_changed README

Change-Id: Iab1001466cb6d2bb0bd46cbc67cf3f1f4ecbcea1

release_changed/README.md

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+release_changed
+===============
+
+App keeps track of the [check-ngcp-release-changes](https://jenkins.mgm.sipwise.com/job/check-ngcp-release-changes) job result and
+[matrix-runner](https://jenkins.mgm.sipwise.com/job/daily-build-matrix-runner/)
+queries the API in order to decide if VM has to be built depending on if the repository has changed since the last successful VM built.