fix for non-existing folder

contribute.py

@@ -20,6 +20,10 @@ def main(date, name):
     # get the root directory
     rootDir = os.getcwd()
 
+    # create a root directory if not existing
+    if not os.path.exists(mainDir):
+        os.mkdir(mainDir)
+
     # generate the full name of the presentation
     fullName = date + "_" + name