added some sources

README.md

@@ -11,3 +11,11 @@ Git for summerstudent project on evolution of open cluster
 * Ask someone to send us a couple of review papers on clusters
 * Write up a more solid form of the project description
 * 
+
+
+# Sources:
+* https://www.sns.ias.edu/tremaine/lectures/ast513/globular
+* http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991ARA%26A..29..543H&db_key=AST&high=384ab081c814843
+* http://adsabs.harvard.edu/abs/2013MNRAS.432.2779B
+* http://adsabs.harvard.edu/abs/2019arXiv190207718B
+