Updating the README file to cite the Xeber point case study.

README.md

@@ -93,6 +93,9 @@ Here is a list of the current case studies:
       Gathering: a Certified Algorithm*. Bonnet, François, Bramas,
       Quentin, Courtieu, Pierre, Défago, Xavier, Rieg, Lionel,
       Tixeuil, Sebastien, Urbain, Xavier.
+    - [Weber/](CaseStudies/Gathering/InR2/Weber/) case studies of
+      protocols using the Weber point. Contains also the definition of
+      the Weber point and proof of its properties.
 - [Exploration/](CaseStudies/Exploration): Exploration of a ring with stop
   - [ImpossibilityKDividesN.v](CaseStudies/Exploration/ImpossibilityKDividesN.v):
     *Impossibility of exploration of a ring when the number of robots