Add another Hera blog (#899)

**Pull Request Checklist**
- [ ] Fixes #<!--issue number goes here-->
- [ ] Tests added
- [x] Documentation/examples added
- [ ] [Good commit messages](https://cbea.ms/git-commit/) and/or PR
title

**Description of PR**
I recalled this blog exists, so adding it to the README

Signed-off-by: Flaviu Vadan <[email protected]>

README.md

@@ -162,6 +162,7 @@ w.create()
 
 ## Blogs
 
+- [Data Validation with Great Expectations and Argo Workflows](https://towardsdatascience.com/data-validation-with-great-expectations-and-argo-workflows-b8e3e2da2fcc)
 - [Hera introduction and motivation](https://www.dynotx.com/hera-the-missing-argo-workflows-python-sdk/)
 - [Dyno is scaling gene therapy research with cloud-native tools like Argo Workflows and Hera](https://www.dynotx.com/argo-workflows-hera/)