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

modules/conga/example_test.go

@@ -174,3 +174,11 @@ func TestDocsDispatch(t *testing.T) {
 		time.Sleep(25 * time.Millisecond)
 	}
 }
+
+func ExampleDescribe() {
+	job := conga.Job(func(ctx context.Context, args ImportPostsArgs) error { return nil },
+		conga.OnQueue("imports"), conga.Timeout(4*time.Minute))
+	info, ok := conga.Describe(job)
+	fmt.Println(ok, info.Kind, info.Queue, info.MaxAttempts, info.Timeout)
+	// Output: true acme_blog_import_posts imports 0 4m0s
+}