feat(14-02): conga.Describe reports a registered job's kind, queue, attempts and timeout

- lets a plugin test assert what its Jobs() registers, such as the CSV
  match job's 240 s timeout, without reaching into conga internals
- README API table, jobs docs page and an example

docs/services/jobs.md

@@ -51,6 +51,8 @@ The options set the job's defaults:
 | `conga.MaxAttempts` | How many times the job is tried before its row is marked as an error. | `queue.max_attempts` (3) |
 | `conga.Timeout` | The deadline of each attempt. | `queue.job_timeout` (300 seconds) |
 
+`conga.Describe` reports a job's kind and these defaults, so a plugin test can assert what its `Jobs()` registers, for example that a long job keeps its `conga.Timeout`.
+
 `conga.JobID` returns the `summer_jobs` row of the running job. It reports `false` when the job has no row, as in the example above, where the function is called directly rather than by a worker.
 
 ## Registering jobs