Update index.html and styles.css

[rmontesdeoca81]

Addressing #1

This pull request includes several changes to the index.html and styles.css files to update the content and improve the styling. The most important changes include adding a new Octocat image, updating the text, and enhancing the CSS for better readability and layout.

Content updates in index.html:

• Added a new Octocat image with the id of octocat and updated the text to "Ready to team up? Let's collaborate, @octocat!" (index.html).

Styling enhancements in styles.css:

• Added new CSS rules for p to set the text color to #333, line height to 1.5, and text alignment to center (styles.css).
• Added new CSS rules for body to set a modern font family and background color (styles.css).
• Added new CSS rules for #octocat img to ensure the image is responsive (styles.css).