Adding Colab Notebook Support and "Open in Colab" Button to README

[DevinduDh]

This pull request adds support for running the repository in Google Colab and includes an "Open in Colab" button in the README file. The changes made are as follows:

1. Created a new Colab notebook (colab-notebook.ipynb) to run the repository.
2. Added the necessary code and instructions to the notebook for running the project.
3. Updated the README file to include a button that allows users to directly open the notebook in Colab.
4. The button is displayed as a badge with the text "Open In Colab" and is linked to the Colab notebook URL.
5. The Colab notebook URL (https://colab.research.google.com/github/DevinduDh/Human-Fall-Detection/blob/master/colab-notebook.ipynb) is properly configured in the button code.
6. These changes make it easier for others to run and interact with the project by providing a convenient way to open the notebook in Colab.
   Please review and merge this pull request to incorporate these enhancements into the repository.

Thank you!