docs(readme): fix contradictory cron wording for check-for-update.yaml

Earlier in this PR the badge table was removed and the CI Status section
gained an on-demand note, but the "Updates → Prisma" paragraph still
described `check-for-update.yaml` as a 5-minute cron job. Rewrite that
paragraph so it matches the rest of the README: the workflow runs on
demand from the Actions tab or via `gh workflow run`.

Author: wmadden

README.md

@@ -39,7 +39,7 @@ Renovate is enabled for this repository for all dependencies except `prisma` and
 
 #### Prisma
 
-When there is a new version, [Prismo](https://github.com/prisma-bot) works tirelessly to commit and push a bump commit, triggering the tests. This is implemented in `.github/workflows/check-for-update.yaml` using a GitHub Action cron job. Since the cron job is limited to run each 5 minutes, we just run each cron job for exactly 5 minutes and check for updates each 10 seconds in each run. This check only runs in the default branch `dev`.
+When there is a new version, a bump commit can be applied to trigger the tests. This is implemented in `.github/workflows/check-for-update.yaml`, which runs only on the default branch `dev`. The workflow is triggered on demand from the [Actions tab](https://github.com/prisma/ecosystem-tests/actions) or via `gh workflow run check-for-update.yaml`.
 
 ### Branches and npm channels