write blog post about Substrait donation

Draft: https://docs.google.com/document/d/1vK0AyDBhIibmKZ2scGN3jBypBvqMPuztbBzZ1eh0dKM/edit?usp=sharing

Start with the linked Google Docs draft to understand the proposed Substrait donation blog post. Then identify the repository's expected location and publishing process for blog content; done means the draft is incorporated as a completed blog post in that location.

Written by the indexing model from the issue text.