docs(tvix): update README to document usage inside tvix view r/5812

If the tvix view is cloned through josh, you don't use mg, but a
`shell.nix` is provided.

Also, add the `git clone` command, so people browsing tvix source code
in the browser know where to clone from.

Change-Id: I18483d6a52953f9f4eafd1533ea69afb0e329b04
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8001
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions