Added "yarn" and "npm" steps in CONTRIBUTING.md

Added the steps to use while setting up an environment using "yarn" and "npm" depending on user preference.

CONTRIBUTING.md

@@ -10,7 +10,7 @@ for a friendly and welcoming collaborative environment.
 Note: You will need NodeJS to build the extension package.
 
 The `jlpm` command is JupyterLab's pinned version of [yarn](https://yarnpkg.com/) that is installed with JupyterLab. You may use
-`yarn` or `npm` in lieu of `jlpm` below.
+`yarn` or `npm` mentioned as an alternative, in lieu of `jlpm` below.
 
 **Note**: we recommend using `mamba` to speed the creating of the environment.
 
@@ -62,6 +62,47 @@ Config dir: /usr/local/etc/jupyter
 
 Then start Jupyter Notebook with:
 
+```bash
+jupyter notebook
+```
+### Alternative : Using "yarn" and "npm" over "mamba" 
+
+If you prefer using `yarn` or `npm` over `mamba`, you can follow these steps to set up your development environment:
+
+Clone the Repository:
+```bash
+git clone https://github.com/jupyter/notebook.git
+cd notebook
+```
+
+Install NodeJS Dependencies:
+If you're using `yarn`:
+```bash
+yarn install
+```
+If you're using `npm`:
+```bash
+npm install
+```
+### Set Up a Python Virtual Environment:
+As the Jupyter Notebook includes a Jupyter Server extension written in Python, it's recommended to create a virtual environment. You can use the `venv` module for this:
+```bash
+python -m venv venv
+source venv/bin/activate  # On Windows, use: venv\Scripts\activate
+```
+Install Python Dependencies:
+```bash
+pip install -e ".[dev,test]"
+```
+Build the Notebook:
+```bash
+jlpm build
+```
+Enable the Server Extension:
+```bash
+jupyter server extension enable notebook
+```
+Start Jupyter Notebook:
 ```bash
 jupyter notebook
 ```