Document how to export CF service creds for the --no-dry-run path

Author: Aguiardavidm

scripts/README.md

@@ -46,6 +46,16 @@ Add `--no-dry-run` to actually trigger the jobs; that path also needs
 `CF_API_URL`, `CF_SERVICE_USER`, and `CF_SERVICE_AUTH` set, since it uses
 `CFHandler` to throttle against `HARVEST_RUNNER_MAX_TASKS`.
 
+These are already set on the deployed app, so pull them from there instead of
+hunting for the underlying service account credentials. `cf env` prints them
+in two different shapes (`CF_API_URL` as a flat `KEY: value` line,
+`CF_SERVICE_USER`/`CF_SERVICE_AUTH` as quoted JSON fields), so a plain
+`grep`/`export` won't catch all three:
+
+```bash
+eval "$(cf env datagov-harvest | grep -E '"?(CF_API_URL|CF_SERVICE_USER|CF_SERVICE_AUTH)"?:' | sed -E 's/^[[:space:]]*"?([A-Z_]+)"?:[[:space:]]*"?([^",]*)"?,?$/export \1="\2"/')"
+```
+
 ### Connecting to the prod database
 
 cloud.gov databases aren't reachable directly from a local machine, so you