Docs/DocBook: Add .db files to .gitignore
Docs/DocBook: Add .db files to .gitignore

These files were added with the XML crossreference patch; they make git
complain.

Signed-off-by: Jonathan Corbet <b2ce64d5587c02f12e367eac59751145a0660c51@lwn.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs