### Summary
The New Contributor Guide added in [this
PR](https://github.com/pytorch/executorch/pull/9977) had an inaccuracy,
mentioned in [this
comment](https://github.com/pytorch/executorch/pull/9977#discussion_r2036181251)
from @byjlw. The guide mistakenly said that only core contributors can
merge PRs.

This PR corrects that error. It encourages the reader to merge their PR
themselves once approved, and provides illustrative screenshots.

Co-authored-by: jhelsby <[email protected]>