Added Reference in Readme

README.md

@@ -14,7 +14,7 @@ through TAP and PYVO services.
 Dependencies: numpy, scipy, pandas, pyvo
 
 To install pyvo: 
->sudo pip install pyvo
+>sudo pip3 install pyvo
 
 Example of session with TAP: selection of a list of cases
 
@@ -49,3 +49,9 @@ Example of session with TAP: download of a fits map of temperatures
 
 >MAP=atap.get_map(tab.URL[0])
 
+REFERENCES:
+Please quote
+Climate bistability of Earth-like exoplanets
+Murante G., Provenzale A., Vladilo G.,Taffoni G., Silva L., Palazzi E.,von Hardenberg J.,Maris M., Londero E., Knapic C., Zorba C.
+MNRAS 492, 2638–2650 (2020) 
+doi: 10.1093/mnras/stz3529