Doc: add download link and script in orca installation. (intel#6750)

* feat: add download orca in installation.

* fix: fix wording.

* fix: fix typo.

* fix: fix wording.

* fix: fix link and add scripts.

* fix: fix wording.

* fix: fix wording.

* fix: add empty check for env variables.

* fix: fix echo.

* fix: update download link

* fix: fix style.

* fix: fix style.

* fix: fix wording and style.

* fix: fix style.

* fix: fix style.

* fix: fix style.

docs/readthedocs/source/doc/Orca/Overview/install.md

@@ -44,6 +44,8 @@ conda activate py37
 ---
 ## Install BigDL Orca
 
+This section demonstrates how to install BigDL Orca via `pip`, which is the most recommended way.
+
 ### To use basic Orca features
 You can install Orca in your created conda environment for distributed data processing, training and inference with the following command:
 ```bash
@@ -121,3 +123,13 @@ pip uninstall bigdl-orca-spark3 bigdl-dllib-spark3 bigdl-tf bigdl-math bigdl-cor
 ```
 
 __Note__: If necessary, you need to manually uninstall `pyspark` and other [dependencies](https://github.com/intel-analytics/BigDL/tree/main/python/requirements/orca) introduced by Orca.
+
+---
+## Download BigDL Orca
+
+You can also download the BigDL package via the download links below. Besides, you can use the [script](https://github.com/intel-analytics/BigDL/blob/main/scripts/download-bigdl.sh) to download.
+
+|           | BigDL 2.1.0 | BigDL 2.2.0-SNAPSHOT nightly |
+| :-------: | :---------: | :--------------------------: |
+| Spark 2.4 | [download](https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.1.0/bigdl-assembly-spark_2.4.6-2.1.0-fat-jars.zip) | [download](https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.2.0-SNAPSHOT/) |
+| Spark 3.1 | [download](https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.2/2.1.0/bigdl-assembly-spark_3.1.2-2.1.0-fat-jars.zip) | [download](https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.3/2.2.0-SNAPSHOT/) |

docs/readthedocs/source/doc/Orca/Tutorial/yarn.md

@@ -309,7 +309,7 @@ On the __Client Node__:
 export SPARK_HOME=/path/to/spark # the folder path where you extract the Spark package
 export SPARK_VERSION="downloaded spark version"
 ```
-2. Download and unzip a BigDL assembly package from [BigDL Assembly Spark 2.4.6](https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_2.4.6/2.1.0/bigdl-assembly-spark_2.4.6-2.1.0-fat-jars.zip) or [BigDL Assembly Spark 3.1.2](https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_3.1.2/2.1.0/bigdl-assembly-spark_3.1.2-2.1.0-fat-jars.zip) (according to your Spark version), then setup the environment variables `${BIGDL_HOME}` and `${BIGDL_VERSION}`.
+2. Refer to [here](../Overview/install.html#download-bigdl-orca) to download and unzip a BigDL assembly package. Make sure the Spark version of your downloaded BigDL matches your downloaded Spark. Then setup the environment variables `${BIGDL_HOME}` and `${BIGDL_VERSION}`.
 ```bash
 export BIGDL_HOME=/path/to/unzipped_BigDL
 export BIGDL_VERSION="downloaded BigDL version"

scripts/download-bigdl.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+
+#
+# Copyright 2016 The BigDL Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+set -x
+
+if [ -z "$BIGDL_VERSION" ]; then
+  echo "Please specify BIGDL_VERSION, e.g. 2.1.0, 2.2.0-SNAPSHOT."
+  exit 1
+fi
+
+echo $BIGDL_VERSION
+
+if [ -z "$SPARK_VERSION" ]; then
+  echo "Please specify SPARK_VERSION, e.g. 2.4.6, 3.1.2 and 3.1.3."
+  exit 1
+fi
+
+echo $SPARK_VERSION
+
+if [[ $BIGDL_VERSION == *"SNAPSHOT"* ]]; then
+  NIGHTLY_VERSION=$(echo $(echo `wget -qO - https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_$SPARK_VERSION/$BIGDL_VERSION/maven-metadata.xml | sed -n '/<value>[0-9]*\.[0-9]*\.[0-9]*-[0-9][0-9]*\.[0-9][0-9]*-[0-9][0-9]*.*value>/p' | head -n1 | awk -F'>' '{print $2}' | tr '</value' ' '`))
+  wget https://oss.sonatype.org/content/repositories/snapshots/com/intel/analytics/bigdl/bigdl-assembly-spark_$SPARK_VERSION/$BIGDL_VERSION/bigdl-assembly-spark_$SPARK_VERSION-$NIGHTLY_VERSION-fat-jars.zip
+  unzip bigdl-assembly-spark_$SPARK_VERSION-$NIGHTLY_VERSION-fat-jars.zip -d $BIGDL_HOME
+else
+  wget https://repo1.maven.org/maven2/com/intel/analytics/bigdl/bigdl-assembly-spark_$SPARK_VERSION/$BIGDL_VERSION/bigdl-assembly-spark_$SPARK_VERSION-$BIGDL_VERSION-fat-jars.zip
+  unzip bigdl-assembly-spark_$SPARK_VERSION-$BIGDL_VERSION-fat-jars.zip -d $BIGDL_HOME
+fi