Add note about using multimod to the release doc (#4280)
Add note about using multimod to the release doc (#4280)

Adding info about running multimod as part of the release process. Also fixing
a typo in the repo name used to produce the changelog in the core repo steps.

Fixes #4204
open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector,open-telemetry/opentelemetry-collector