Update README (#619)

* Update README 

Fixes https://github.com/Azure/azure-functions-sql-extension/issues/408. Documenting that the table cannot contain two columns that only differ by case.

* Update README.md

Co-authored-by: Charles Gagnon <chgagnon@microsoft.com>

Co-authored-by: Charles Gagnon <chgagnon@microsoft.com>

README.md

@@ -42,6 +42,7 @@ This extension uses the [OPENJSON](https://learn.microsoft.com/sql/t-sql/functio
 Databases on SQL Server, Azure SQL Database, or Azure SQL Managed Instance which meet the compatibility level requirement above are supported.
 
 ## Known Issues
+- The table used by a SQL binding or SQL trigger cannot contain two columns that only differ by casing (Ex. 'Name' and 'name'). 
 
 ### Output Bindings
 - Output bindings against tables with columns of data types `NTEXT`, `TEXT`, or `IMAGE` are not supported and data upserts will fail. These types [will be removed](https://docs.microsoft.com/sql/t-sql/data-types/ntext-text-and-image-transact-sql) in a future version of SQL Server and are not compatible with the `OPENJSON` function used by this Azure Functions binding.