Add Phi-3 on device announcement (#20740)
### Description
Add announcement with link to Phi-3 On-Device blog on Hugging Face site
Staged here:
https://sophies927.github.io/onnxruntime/blogs/phi-3-on-device
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
