Update versioning introduction documentation

https://github.com/conan-io/docs/blob/master/versioning/introduction.rst

From my point of view, this page is missing other important version conflicts:

1. 'Build requires' version conflict
There is one more version conflict type. What if PkgB or PkgC is not a regular dependency, but it comes from 'build_requires' method? There is no solution for this so far for this type of conflict.

2. Conflict about the recipe with the same functionality
some recipes may implement the same api. For example, ‘libjpeg' and ‘libjpeg-turbo'. It’s not allowed to have different implementations of the same api across the whole project. Unfortunately, it’s not possible to override it in the root recipe.