Doc: add instruction to build doc.

docs/source/development/doc.md

+# How to contibute to Documentation
+
+The CEPCSW user guide is created using a tool called sphinx. Sphinx could parse the Markdown files and then create HTML files. The Markdown files are all maintained in the source code of CEPCSW.
+
+Here is an instruction to add or modify the user guide:
+* Fork the CEPCSW and git clone the source code
+```bash
+$ git clone git@code.ihep.ac.cn:cepc/CEPCSW.git
+$ cd CEPCSW/docs/
+```
+* Add or modify the markdown files
+  * If you need to add new pages, please add file names in the index.rst. 
+* If sphinx is not available, you need to install it and its dependencies. See the below instructions.
+```bash
+$ python -m venv venv             # create a virtual environment
+$ source venv/bin/activate        # activate the venv
+$ pip install -r requirements.txt # install the dependencies
+```
+* Build the user guide with sphinx
+```bash
+$ make html
+```
+* Run a lightweight web server using python. 
+  * The URL will consists of two parts: server name and port number. 
+  * Use the command `hostname` to get the name of the server name. If you build the docs in your local computer, just use `localhost`.
+  * If the port number `8888` is already used by others, just change to some other number. 
+  
+```bash
+$ python -m http.server 8888 --bind 0.0.0.0 --directory build/html
+```
+* Use Web Browser to view the document. 
+  * For example: http://localhost:8888
+* If there is no issue, then `git commit` and `git push`. Create a MR when it is ready.  

docs/source/development/overview.md

 # Development Process Overview
 
-Under construction.
+Modern HEP experiments (usually long timescale) are large distributed collaborations with several hundred people. The software project should be managed properly and the code quality is important.
\ No newline at end of file
+
+Software development life cycle consists of
+* Planning
+* Analysis and Design
+* Implementation
+* Testing and Integration
+* Maintenance
+
+Best Practices in the open source communities:
+* Building software -> CMake
+* Source code control -> Git and Pull/Merge Request workflow
+* Continuous integration -> GitHub Actions or GitLab CI
+* Software distribution -> package management tools and apptainer containers
+* Training and documentation -> sphinx

docs/source/index.rst

@@ -23,6 +23,7 @@ Contents
    :caption: Development Process
 
    development/overview.md
+   development/doc.md
 
 .. toctree::
    :maxdepth: 2