add logo

Author: Mei-Hui Su

README.md

@@ -1,5 +1,7 @@
 # San Francisco Community Velocity Model (sfcvm)
 
+<a href="https://github.com/sceccode/sfcvm.git"><img src="https://github.com/sceccode/sfcvm/wiki/images/sfcvm_logo.png"></a>
+
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