Write a description for the SQL and Databases Module

[Tammy Robinson]

@mattstauffer Let me know if this is good or if you have suggestions:

Learn to store, query, and manipulate your application's data using SQL.

[Andrew Morgan]

@tammytee I think what you have here is good although I changed manipulate to modify. I went ahead and updated it in Nova.

[Tammy Robinson]

Thanks @andrewmile!