Improve Release-Process "updating-the-changelog"

[pljones]

Describe the bug

https://jamulus.io/contribute/Release-Process#updating-the-changelog should mention checking the existing "next release" and confirming it's correct before proceeding.

To Reproduce

Run the change log too with x.y.1 when the next release is x.z.0

Expected behavior

The person running the change log should have been told to commit to jamulus/jamulus/main a corrected version of the change log prior to running the tool.