tweak contributing doc to explain the correct np invocation

CONTRIBUTING.md

@@ -109,6 +109,8 @@ We publish using `np`: https://npm.im/np
 2. Rebuild the README (see instructions above, necessary because npmjs.com renders the readme)
 3. (optional) Update the api-extractor report; check for unexpected changes.  See below
 4. Publish with `np`
+ - `np --branch main --no-tests`
+  - `--no-tests` because we must rely on CI to test ts-node.  Even if you *did* run the tests locally, you would only be testing a single operating system, node version, and TypeScript version, so locally-run tests are insufficient.
 5. Add changelog to the Github Release; match formatting from previous releases
 6. Move `docs` branch to head of `main`
   - this rebuilds the website