add warning about cleartext password into PuttySSHVendor

dulwich/client.py

@@ -1154,6 +1154,11 @@ class PuttySSHVendor(SSHVendor):
             args = ['putty', '-ssh']
 
         if password:
+            import warnings
+            warnings.warn(
+                "Putty show you password in clear text "
+                "in the list of arguments, so use ParamikoSSHVendor "
+                "instead if you care about security")
             args.extend(['-pw', str(password)])
 
         if port: