Add seed: RCN list file

[juzraai]

What problem this feature would solve (e.g. who needs it and why)

One may collect RCNs by hand into a spreadsheet, it may be difficult to generate a -s rcn1,rcn2,... list.

How would it solve it

It would be easier to export the RCN column or the whole spreadsheet to a text file, then tell the crawler to read RCNs from there.

How do you imagine using the feature (e.g. CLI configuration, output format)

-s file.tsv,1 seed argument would tell the crawler to read file.tsv as a TSV file and search for RCNs in the first column. Let's use 1-based indexes here.

The column index can be optional with default value 1.

We can accept both *.tsv and *.txt file extensions.

The reader would iterate the file line-by-line and would skip non-number values.