I believe your CSV file will need a couple alterations. First, I don't think Exiftool will read a tab delimited csv. The docs seem to indicate comma separated only. You could import into Excel or OpenOffice with the tab delimiter set and export a new CSV which should be readable to Exiftool.
Second, the first line needs to needs to have column headers indicating the Tags you want to import. The first column needs to be SourceFile. Your second column could be Keywords (for IPTC:Keywords) or Subject (for XMP:Subject). I'd suggest Subject, as that's the more modern standard. I believe LR will read either and will write both.
After that, the command should be something like
Exiftool -sep ", " -csv=/path/to/file.csv /path/to/target/files
If the files are in multiple directories, just add those directories. You can add
-r to recurse. Exiftool should only process those files in the CSV file and are included in the command line directories.
-sep option indicates the value that should be used to separate each item of the keywords.
Exiftool docs on -csv
Exiftool FAQ 26, How do I import information from a database?