[eventgrid] Update README.md
Fix broken pip link by adding missing reference to
@@ -223,6 +223,7 @@ This project has adopted the [Microsoft Open Source Code of Conduct][code_of_con
[python-eg-ref-docs]: https://aka.ms/azsdk/python/eventgrid/docs
[python-eg-samples]: https://github.com/Azure/azure-sdk-for-python/tree/master/sdk/eventgrid/azure-eventgrid/samples
[python-eg-changelog]: https://github.com/Azure/azure-sdk-for-python/tree/master/sdk/eventgrid/azure-eventgrid/CHANGELOG.md
+[pip]: https://pypi.org/project/pip/
[azure_portal_create_EG_resource]: https://ms.portal.azure.com/#blade/HubsExtension/BrowseResource/resourceType/Microsoft.EventGrid%2Ftopics
[azure-key-credential]: https://aka.ms/azsdk/python/core/azurekeycredential
