Update README.md

README.md

-For more information about theC(canonical) Scan Matcher, see the webpage: http://purl.org/censi/2007/csm.
+For more information about the C(anonical) Scan Matcher, see the webpage: http://purl.org/censi/2007/csm.
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+Note: there are two branches on the repository. The "master" branch uses GSL.
+
+This is the ``csm_eigen`` branch, which uses the ``eigen`` library. 
+This branch is the work of people working at U. Freiburg and Kuka, 
+including Christoph Sprunk and Rainer Kuemmerle.