cherry pick pingcap#2828 to release-1.1

Signed-off-by: ti-srebot <ti-srebot@pingcap.com>

docs/api-references/docs.md

@@ -3453,6 +3453,19 @@ bool
 <em>(Optional)</em>
 </td>
 </tr>
+<tr>
+<td>
+<code>disable-telemetry</code></br>
+<em>
+bool
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>When not disabled, usage data will be sent to PingCAP for improving user experience.
+Optional: Defaults to false</p>
+</td>
+</tr>
 </tbody>
 </table>
 <h3 id="discoveryspec">DiscoverySpec</h3>
@@ -9475,8 +9488,8 @@ bool
 </em>
 </td>
 <td>
-<p>imported from v3.1.0
-optional</p>
+<em>(Optional)</em>
+<p>imported from v3.1.0</p>
 </td>
 </tr>
 <tr>
@@ -9487,8 +9500,24 @@ uint64
 </em>
 </td>
 <td>
-<p>imported from v3.1.0
-optional</p>
+<em>(Optional)</em>
+<p>imported from v3.1.0</p>
+</td>
+</tr>
+<tr>
+<td>
+<code>enable-telemetry</code></br>
+<em>
+bool
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>When enabled, usage data (for example, instance versions) will be reported to PingCAP periodically for user experience analytics.
+If this config is set to <code>false</code> on all TiDB servers, telemetry will be always disabled regardless of the value of the global variable <code>tidb_enable_telemetry</code>.
+See PingCAP privacy policy for details: <a href="https://pingcap.com/en/privacy-policy/">https://pingcap.com/en/privacy-policy/</a>.
+Imported from v4.0.2.
+Optional: Defaults to true</p>
 </td>
 </tr>
 </tbody>