00-sql-introduction.md: steps under "import" not clear

[michielcock]

The steps under "Import" are not completely clear: it doesn't mention that you specify the location where your database needs to be saved.
Also, it assumes in step 6 and 10 that you have seen the content of the database: how do I know whether the first row has column headings or what columns contain which data type if I haven't seen the file? Better explain how to get a quick overview of the contents.