docs: add reference to DELPHI performance paper

data/docs/delphi-about/delphi-about.md

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-DELPHI was one of four large detectors on the Large Electron-Positron collider (LEP). It took 7 years to design and build, and it started up in 1989. In December 2000, DELPHI stopped taking data and was dismantled to leave room for the construction of the Large Hadron Collider in the LEP tunnel. A detailed description of the detector as it was in 1990 can be found in [this preprint](https://cds.cern.ch/record/212026/files/cer-000124113.pdf), which has been published in [Nuclear Instruments and Methods, A303 (1991), 233-276](https://doi.org/10.1016/0168-9002%2891%2990793-P).
+DELPHI was one of four large detectors on the Large Electron-Positron collider (LEP). It took 7 years to design and build, and it started up in 1989. In December 2000, DELPHI stopped taking data and was dismantled to leave room for the construction of the Large Hadron Collider in the LEP tunnel. A detailed description of the detector as it was in 1990 can be found in [this preprint](https://cds.cern.ch/record/212026/files/cer-000124113.pdf), which has been published in [Nuclear Instruments and Methods, A303 (1991), 233-276](https://doi.org/10.1016/0168-9002%2891%2990793-P). For the LEP2 period, there is an [updated version available on CDS](https://cds.cern.ch/record/295267), which also includes performance data.
 
 ## Overview
 The DELPHI detector consisted of a central cylinder filled with subdetectors, with two end-caps. It was 10 meters in length and diameter, and weighed 3500 tons. The detector consisted of 20 subdetectors. A large superconducting magnet sat between an electromagnetic calorimeter and a hadronic calorimeter. The magnet generated a field to deflect charged particles so their charge and momenta could be measured.