[Chapel Merge] add file to README

Branch: refs/heads/main
Revision: 25b0f7c6fed5809bfa2114b9eeb91888911d82fd
Author: stonea
Link: add file to README by stonea · Pull Request #25635 · chapel-lang/chapel · GitHub
Log Message:
add file to README (#25635)

Looks like we have a script that checks README files under dirs under
test/release/examples/. This script requires that the README mention
every .chpl file under that dir.

In #25562 I added this README but didn't mention the hello-gpu.chpl
file I added. This PR should fix that.

[Reviewed by nobody; simple doc update]

Compare: Comparing 790677e14c1f557efcc716cd3cf1a89348535c1e...86af8c8f78660f07100158bdd3e003105f26a980 · chapel-lang/chapel · GitHub

Diff:
M test/release/examples/gpu/README
https://github.com/chapel-lang/chapel/pull/25635.diff