[docs] set chng flu earliest available dates

Author: krivard

docs/api/covidcast-signals/chng.md

@@ -33,8 +33,8 @@ commercial purposes.
 | `smoothed_adj_outpatient_covid` | Same, but with systematic day-of-week effects removed; see [details below](#day-of-week-adjustment) <br/> **Earliest date available:** 2020-02-01 |
 | `smoothed_outpatient_cli` | Estimated percentage of outpatient doctor visits primarily about COVID-related symptoms, based on Change Healthcare claims data that has been de-identified in accordance with HIPAA privacy regulations, smoothed in time using a Gaussian linear smoother <br/> **Earliest date available:** 2020-02-01 |
 | `smoothed_adj_outpatient_cli` | Same, but with systematic day-of-week effects removed; see [details below](#day-of-week-adjustment) <br/> **Earliest date available:** 2020-02-01 |
-| `smoothed_outpatient_flu` | Estimated percentage of outpatient doctor visits with confirmed influenza, based on Change Healthcare claims data that has been de-identified in accordance with HIPAA privacy regulations, smoothed in time using a Gaussian linear smoother <br/> **Earliest date available:** 2021-10-01 |
-| `smoothed_adj_outpatient_flu` | Same, but with systematic day-of-week effects removed; see [details below](#day-of-week-adjustment) <br/> **Earliest date available:** 2021-10-01 |
+| `smoothed_outpatient_flu` | Estimated percentage of outpatient doctor visits with confirmed influenza, based on Change Healthcare claims data that has been de-identified in accordance with HIPAA privacy regulations, smoothed in time using a Gaussian linear smoother <br/> **Earliest issue available:** 2021-12-06 <br/> **Earliest date available:** 2020-02-01 |
+| `smoothed_adj_outpatient_flu` | Same, but with systematic day-of-week effects removed; see [details below](#day-of-week-adjustment) <br/> **Earliest issue available:** 2021-12-06 <br/> **Earliest date available:** 2020-02-01 |
 ## Table of Contents
 {: .no_toc .text-delta}