Add Mercedes-Benz to sponsor list

Add Mercedes-Benz to the README as one of our generous sponsors.

Author: ericwb

README.rst

@@ -127,6 +127,11 @@ The development of Bandit is made possible by the following sponsors:
    :width: 100%
    :class: borderless
 
+   * - .. image:: https://avatars.githubusercontent.com/u/34240465?s=200&v=4
+          :target: https://opensource.mercedes-benz.com/
+          :alt: Mercedes-Benz
+          :width: 88
+
    * - .. image:: https://github.githubassets.com/assets/tidelift-8cea37dea8fc.svg
           :target: https://tidelift.com/lifter/search/pypi/bandit
           :alt: Tidelift