Add database-compatibility-matrix to readme

[hsorbo]

Based on comments like this i suggest a compatiblity matrix in the readme under the section Will Dapper work with my DB provider?.

This way new users can get some heads-up before investing time and effort. Especially Microsoft.Data.Sqlite seem to have long standing issues breaking a lot of use-cases and should be worthy of a caution.

[jonreis]

Does Dapper support Microsoft.Data.Sqlite? I am having a hell of a time moving to it from System.Data.Sqlite.

[NickCraver]

I'm not sure this would belong in the README, but a dedicated doc perhaps. Given this depends on the providers which shift underneath us though it'd be nature be a best effort list of caveats.