added Version 3 to the README.md file

RU/README.md

 Documentation: 
 The CRIS NASA L1B Products and documentation, including 
 the NASA Cross-track Infrared Sounder (CrIS) Level 1B Radiometric 
-Uncertainty Description Document can be found at the following DOIs:
+Uncertainty Description Document (Version 3) can be found at the 
+following DOIs:
 
 -  SNPP NSR Version 3: https://doi.org/10.5067/OZZPDWENP2NC
 -  SNPP FSR Version 3: https://doi.org/10.5067/ZCRSHBM5HB23