Syntax: an HTTP URL to a plain text file (not HTML)
This may be used to specify the URL for a plain text file containing URLs
for individual pages. In the file, the list of URLs can be one URL per line (preferred) or delimited by any number of spaces.
If you change this and click "Update" instead of "GO" the added pages
will be fetched immediately and added to the existing database.
The file itself is not checked for changes, and pages removed from the
file will NOT be removed from the database until the next rewalk.
