[SPARK-3766][Doc]Snappy is also the default compress codec for broadc…

…ast variables

Author: scwf <wangfei1@huawei.com>

Closes apache#2632 from scwf/compress-doc and squashes the following commits:

7983a1a [scwf] snappy is the default compression codec for broadcast

docs/configuration.md

@@ -413,10 +413,11 @@ Apart from these, the following properties are also available, and may be useful
   <td><code>spark.io.compression.codec</code></td>
   <td>snappy</td>
   <td>
-    The codec used to compress internal data such as RDD partitions and shuffle outputs. By default,
-    Spark provides three codecs: <code>lz4</code>, <code>lzf</code>, and <code>snappy</code>. You
-    can also use fully qualified class names to specify the codec, e.g.
-    <code>org.apache.spark.io.LZ4CompressionCodec</code>,
+    The codec used to compress internal data such as RDD partitions, broadcast variables and
+    shuffle outputs. By default, Spark provides three codecs: <code>lz4</code>, <code>lzf</code>,
+    and <code>snappy</code>. You can also use fully qualified class names to specify the codec, 
+    e.g. 
+    <code>org.apache.spark.io.LZ4CompressionCodec</code>,    
     <code>org.apache.spark.io.LZFCompressionCodec</code>,
     and <code>org.apache.spark.io.SnappyCompressionCodec</code>.
   </td>