#187 Add details on interactions between Scala and Kryo

[arnaud-daroussin]

As describe in the issue and this comment #187 (comment), here is a proposal to add more details of interactions between Scala and Kryo and explain the case where the duplication of case objects can occur.

First point of comment is addressed by adding some context:

- has no silent fallback to Kryo: it will just fail the compilation in a case when serializer cannot be made
+ `TypeInformation` derivation macro has no silent fallback to Kryo: it will just fail the compilation in a case when serializer cannot be made

Second point:

• add explanations in "Supported Flink versions" section where the suggestion of removing flink-scala dependency was made.
• Add more details in new "Interaction with Flink's type system" section, with an explicit warning when flink-scala dependency is removed and Kryo is used.

As a first step for the third point, recommend to disable Kryo to fail-fast, at least in a test environment.

[novakov-alexey]

Perfect. Thank you very much for this explanation, @arnaud-daroussin .