WIP Update cms-external-resources.xml

Trying to address https://github.com/cernopendata/opendata.cern.ch/pull/493#issuecomment-60944042
Will fix the link to the dataset
In Comment https://github.com/cernopendata/opendata.cern.ch/pull/493#issuecomment-60944042 you suggest to make it also a record in the Instructions collection and as from my point of view, the record looks the same, I thought I just attach the PDFs here and add it to a second collection. Also as this will make linking easier as one only has to link to one record and might be less confusing for users who are not aware of the difference between the collections.