Change database.md tech notes to recommend install of SQLite Viewer extension

[mandyWW]

The SQLite Viewer for VSCode extension provides an easy way for students to look at their database. Hence we could recommend using this in the tech notes instead of installing SQLite.

[davewhiteland]

Roger this — I am holding off making any edits to the upstream tech notes while we're running this term's RHUL project to avoid any conflicts with your local tech_notes edits, to keep pulling my upstream code changes straightforward. We'll pull things like this in at the end of term.