add release doc branch-2.1 (#5980)

* add release doc branch-2.1

* update

Author: Le-Zheng

docs/readthedocs/source/doc/release.md

@@ -1,6 +1,6 @@
 # Release Download
 
-- **Release 2.1.0-SNAPSHOT nightly build**
+- **Release 2.1.0**
 <table border="1"
 cellpadding="10"
 >
@@ -11,13 +11,35 @@ cellpadding="10"
     </tr>
     <tr>
        <td>Spark 2.4.6 </td>
-       <td><a href="https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.1.0-SNAPSHOT/">download</a></td>
-       <td><a href="https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-dllib-spark_2.4.6/2.1.0-SNAPSHOT/">download</a></td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.1.0/">download</a></td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-dllib-spark_2.4.6/2.1.0/">download</a></td>
     </tr>
     <tr>
        <td>Spark 3.1.2 </td>
-       <td><a href="https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.2/2.1.0-SNAPSHOT/">download</a></td> 
-       <td><a href="https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-dllib-spark_3.1.2/2.1.0-SNAPSHOT/">download</a></td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.2/2.1.0/">download</a></td> 
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-dllib-spark_3.1.2/2.1.0/">download</a></td>
+    </tr>
+</table>
+<br>
+
+- **Release 2.0.0**
+<table border="1"
+cellpadding="10"
+>
+    <tr>
+        <td></td>
+        <td>BigDL (All in One)</td>
+        <td>DLlib</td>
+    </tr>
+    <tr>
+       <td>Spark 2.4.6 </td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.0.0/bigdl-assembly-spark_2.4.6-2.0.0.zip">download</a></td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-dllib-spark_2.4.6/2.0.0/">download</a></td>
+    </tr>
+    <tr>
+       <td>Spark 3.1.2 </td>
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.2/2.0.0/bigdl-assembly-spark_3.1.2-2.0.0.zip">download</a></td> 
+       <td><a href="https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-dllib-spark_3.1.2/2.0.0/">download</a></td>
     </tr>
 </table>
 <br>