Add license field to the config file example in "How to publish" page

[magurotuna]

Current "How to publish" page looks like this. Following the instruction, we end up getting missing-lisence error:

error[missing-license]: missing license field or file
 --> /Users/yusuke/Repo/github.com/magurotuna/test-add/deno.json
  = hint: add a "license" field. Alternatively, add a LICENSE file to the package and ensure it is not ignored from being published

  docs: https://jsr.io/go/missing-license

error: Found 1 problem

I think probably there should be "license": "MIT" field in the default example of a config file.