Update documentation for client side certificate

pymisp/api.py

@@ -99,6 +99,7 @@ class PyMISP(object):
         :param out_type: Type of object (json) NOTE: XML output isn't supported anymore, keeping the flag for compatibility reasons.
         :param debug: print all the messages received from the server
         :param proxies: Proxy dict as describes here: http://docs.python-requests.org/en/master/user/advanced/#proxies
+        :param proxies: Client certificate, as described there: http://docs.python-requests.org/en/master/user/advanced/#ssl-cert-verification
     """
 
     # So it can may be accessed from the misp object.