docs(helm): Mention commit signing in the Developer Guide (#5018)
docs(helm): Mention commit signing in the Developer Guide (#5018)

This change adds a mention to the reqruiement for commit signing
to the Git Convention outline in the Developer Guide, while
leaving the existing detail on signing in the Contributing doc.

Closes #5016

Signed-off-by: Henry Nash <0a1d91dd2084cd08cc895b69e65b79edd10f9a30@uk.ibm.com>
appscode/helm,appscode/helm,SlickNik/helm,jascott1/helm,SlickNik/helm,jascott1/helm