Missing `###` from dataset section titles

[alejands]

This is a very quick fix.

NanoProduction/get_nano_files.sh

Line 2 in ab90423

echo "DYJetsToLL" > nano_files.txt

This should match the convention used in PFNano

https://github.com/DeepMETv2/PFNano/blob/13_0_7_from124MiniAOD/deepmet/xrootd_filenames.txt

so an auto-generated file would work "out of the box" with a script like

https://github.com/DeepMETv2/PFNano/blob/13_0_7_from124MiniAOD/deepmet/xrdcp_filelist.py

The version currently saved in this repository already has these additional ### characters, but a new auto-generated file would not include these.

https://github.com/DeepMETv2/NanoProduction/blob/ab90423ea84b68555314a2ba823e04e294d228f1/nano_files.txt