Improve version matrix in documentation to mention mybatis compatibility

[snicoll]

Hello,

Thank you for all the hard work on the starter.

I wonder if having a relationship between the starter and the "mybatis-spring" dependency in the documentation is so important. I might be wrong but I expect that table to provide the mybatis version one should use to use a version of the starter.

For context, I thought the releasing scheme of this starter can be improved. Since October last year, we're still in the 2.1.x line with 2.1.1, 2.1.2, 2.1.3 and recently 2.1.4. But looking at the changelog I was surprised to see that the generation of mybatis did not change. Having that in the doc could help.

I also wonder if harmonizing the version of mybatis-spring and this project would be worthwhile.

Anyway, food for thoughts. Thanks again!