docs: update README.rst

Author: jourdain

README.rst

@@ -1,6 +1,8 @@
-==============
-trame-datagrid
-==============
+.. |pypi_download| image:: https://img.shields.io/pypi/dm/trame-datagrid
+
+==========================================
+trame-datagrid |pypi_download|
+==========================================
 
 Trame widget of the `RevoGrid <https://revolist.github.io/revogrid/>`_ component for vue3.
 
@@ -55,4 +57,4 @@ Community
 Enjoying trame?
 -----------------------------------------------------------
 
-Share your experience `with a testimonial <https://github.com/Kitware/trame/issues/18>`_ or `with a brand approval <https://github.com/Kitware/trame/issues/19>`_.
+Share your experience `with a testimonial <https://github.com/Kitware/trame/issues/18>`_ or `with a brand approval <https://github.com/Kitware/trame/issues/19>`_.