DOC/SEC/MAINT: Update security.md with Tidelift.

Also add badge to readme.

README.rst

@@ -13,6 +13,9 b''
 .. image:: https://raster.shields.io/badge/Follows-NEP29-brightgreen.png
     :target: https://numpy.org/neps/nep-0029-deprecation_policy.html
 
+.. image:: https://tidelift.com/subscription/pkg/pypi-ipython
+    :target: https://tidelift.com/badges/package/pypi/ipython?style=flat
+
 
 ===========================================
  IPython: Productive Interactive Computing

SECURITY.md

@@ -4,3 +4,8 b''
 
 All IPython and Jupyter security are handled via [e-mail]. 
 You can find more information on the Jupyter website. https://jupyter.org/security
+
+## Tidelift
+
+We are also lifting IPython via Tidelift, you can also report security concern via the [tidelift platform](
+https://tidelift.com/security).