docs: add OpenSSF Scorecard badge to README

Links to the scorecard.dev viewer for this repo. Badge image will 404
until the first Scorecard run completes after this PR merges (the
workflow's `push: branches: [main]` trigger fires the first run; the
weekly schedule keeps it refreshed thereafter). Brief broken-badge
window while indexing settles is acceptable; the badge then tracks
supply-chain hygiene drift over time and gives a one-glance status
signal to anyone landing on the repo page.

Signed-off-by: Will Manning <will@willmanning.io>

Author: lwwmanning

README.md

@@ -1,5 +1,7 @@
 # vortex.dev
 
+[![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/vortex-data/vortex.dev/badge)](https://scorecard.dev/viewer/?uri=github.com/vortex-data/vortex.dev)
+
 Source for [vortex.dev](https://vortex.dev), the marketing site for [Vortex](https://github.com/vortex-data/vortex) — an extensible, state-of-the-art columnar file format. Vortex is a [Linux Foundation](https://www.linuxfoundation.org/) incubating project, a Series of LF Projects, LLC.
 
 ## Local development