Add Mistral and Phi to model table

[philippgille]

I was looking into running a good embedding model locally. The popular embedding model leaderboard currently (2024-01-07) shows e5-mistral-7b-instruct as top entry. I checked mlc-llm's README and it didn't seem to support the Mistral architecture. Only when checking the docs that turned out to be wrong.

=> As many people might be quick to leave when not finding Mistral on the README, I propose to include this info on the README directly, instead of only in the docs.

To have a smaller README, maybe some of the other listed models can be removed, which might be less popular?

It might also be worth adding one row with ... or ... (see docs) with a link, to the docs, which might make clearer that people should check the link and it's easier/quicker to see than reading the text paragraph above the table.
If you want, I can adjust this PR accordingly.

[junrushao]

CC: @CharlieFRuan

[CharlieFRuan]

LGTM! Thank you for the suggestions; we'll think about making the README more direct!