[SPARK-16870][DOCS] Summary:add "spark.sql.broadcastTimeout" into docs/sql-programming-gu…

## What changes were proposed in this pull request?
default value for spark.sql.broadcastTimeout is 300s. and this property do not show in any docs of spark. so add "spark.sql.broadcastTimeout" into docs/sql-programming-guide.md to help people to how to fix this timeout error when it happenned

## How was this patch tested?

not need

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

…ide.md

JIRA_ID:SPARK-16870
Description:default value for spark.sql.broadcastTimeout is 300s. and this property do not show in any docs of spark. so add "spark.sql.broadcastTimeout" into docs/sql-programming-guide.md to help people to how to fix this timeout error when it happenned
Test:done

Author: keliang <keliang@cmss.chinamobile.com>

Closes #14477 from biglobster/keliang.

docs/sql-programming-guide.md

@@ -1159,6 +1159,15 @@ that these options will be deprecated in future release as more optimizations ar
       scheduled first).
     </td>
   </tr>
+  <tr>
+    <td><code>spark.sql.broadcastTimeout</code></td>
+    <td>300</td>
+    <td>
+    <p>
+      Timeout in seconds for the broadcast wait time in broadcast joins
+    </p>
+    </td>
+  </tr>
   <tr>
     <td><code>spark.sql.autoBroadcastJoinThreshold</code></td>
     <td>10485760 (10 MB)</td>