Man page says:
-i file
--input-file=file
Read URLs from file. If - is specified as file, URLs are read from
the standard input. (Use ./- to read from a file literally named
-.)
If this function is used, no URLs need be present on the command
line. If there are URLs both on the command line and in an input
file, those on the command lines will be the first ones to be
retrieved. The file need not be an HTML document (but no harm if
it is)---it is enough if the URLs are just listed
sequentially.
Say if you don't use --force-html then it better not be HTML!
However, if you specify --force-html, the document will be regarded
as html. In that case you may have problems with relative links,
which you can solve either by adding "<base href="url">" to the
documents or by specifying --base=url on the command line.
Also one can't use -i file:///bla.html
