docs: clarify that a breaking change, with `allow-initial-development-versions` shouldn't bump the major version

[jamietanna]

It should bump the minor, instead

[christophwitzko]

The idea was that a project could start with the major version 0. Once the project is ready for the v1 release, the author can trigger that by using the breaking change convention. This is also why I called the flag allow-initial-development-versions and not enforce-initial-development-versions. Once v1 or higher has been reached, the flag has no effect anymore.

But I agree with you, the docs should be definitely extended to explain this behavior to its detail.