Update doc style (#6841)

* minor

* trial

* change to dot

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

@@ -46,7 +46,7 @@ conda activate py37
 
 This section demonstrates how to install BigDL Orca via `pip`, which is the most recommended way.
 
-__Note:__
+__Notes:__
 * Installing BigDL Orca from pip will automatically install `pyspark`. To avoid possible conflicts, you are highly recommended to  **unset the environment variable `SPARK_HOME`**  if it exists in your environment.
 
 * If you are using a custom URL of Python Package Index to install the latest version, you may need to check whether the latest packages have been sync'ed with pypi. Or you can add the option `-i https://pypi.python.org/simple` when pip install to use pypi as the index-url.

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

@@ -296,24 +296,25 @@ sc = init_orca_context(cluster_mode="spark-submit")
 ```
 
 Before submitting the application on the __Client Node__, you need to:
-
-1. Prepare the conda environment on a __Development Node__ where conda is available and pack the conda environment to an archive:
+- First, prepare the conda environment on a __Development Node__ where conda is available and pack the conda environment to an archive:
 ```bash
 conda pack -o environment.tar.gz
 ```
-2. Send the Conda archive to the __Client Node__;
+
+- Then send the conda archive to the __Client Node__;
 ```bash
 scp /path/to/environment.tar.gz username@client_ip:/path/to/
 ```
 
-On the __Client Node__:
 
-1. Download and extract [Spark](https://archive.apache.org/dist/spark/). Then setup the environment variables `${SPARK_HOME}` and `${SPARK_VERSION}`.
+On the __Client Node__:
+- Download and extract [Spark](https://archive.apache.org/dist/spark/). Then setup the environment variables `${SPARK_HOME}` and `${SPARK_VERSION}`.
 ```bash
 export SPARK_HOME=/path/to/spark # the folder path where you extract the Spark package
 export SPARK_VERSION="downloaded spark 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}`.
+
+- 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"