doc(shannon): The limitation of ShannonBase

[ShannonBase]

In this part, we will list all the limitation in ShannonBase.
0: Supported the version is great than 8.0. MySQL 5.7 or less is not available.
1: Rapid Engine is mandatory installed. Rapid Engine is a memory column store, used to accelerate AP workloads.
2: Supported data type in Rapid Engine: (1) int, bigint, numeric, double, float; (2) Date, time; (3) char, varchar, text.
3: A table with rapid secondary engine MUST BE has at least ONE user defined primary key, and it's type is numeric supported now.

[ShannonBase]

pls refer to wiki