Added SEO and Social Media Meta Tags

[Aman-G-upta]

This pull request improves the SEO and social media optimization for the Alien Invasion game by adding and refining meta tags in the HTML section. This will enhance search engine visibility, improve social media sharing, and contribute to a better user experience when links are shared across platforms.
Fixes: #605
Changes made :
Added essential SEO meta tags, including description, keywords, and robots.
Added Open Graph tags (og:title, og:description, og:image, og:url, etc.) to optimize how the page appears when shared on social media platforms like Facebook.
Added Twitter card tags to improve appearance on Twitter.
Cleaned up the section by organizing tags for readability and maintainability.

Before

<title>Alien Game</title>

After

<meta name="description" content="Alien Invasion Defense - A thrilling game where you defend Earth from alien invaders 
with power-ups like health boosts, shields, and speed boosts. Join the ultimate gaming experience!">
<meta name="keywords" content="Alien Invasion Defense, alien shooter game, arcade game, defense game, space 
 invaders, alien attack, online gaming, power-ups, gaming experience">
<meta name="robots" content="index, follow">

<meta property="og:title" content="Alien Invasion Defense - Protect Earth from Alien Invaders!">
<meta property="og:description" content="Defend Earth against waves of alien invaders in this action-packed game. 
 Utilize power-ups and upgrade your defenses to survive!">
<meta property="og:image" content="https://example.com/og-image.jpg">
<meta property="og:url" content="https://example.com/alien-invasion-defense">
<meta property="og:type" content="website">

<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:title" content="Alien Invasion Defense - Protect Earth from Alien Invaders!">
<meta name="twitter:description" content="Defend Earth against waves of alien invaders in this action-packed game. Use 
 power-ups and strategies to survive!">
<meta name="twitter:image" content="https://example.com/twitter-image.jpg">
<title>Alien Invasion Defense</title>
<link rel="icon" href="favicon.png" type="image/x-icon">
<link href="https://fonts.googleapis.com/css2?family=Roboto:wght@400;700&display=swap" rel="stylesheet">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.4/css/all.min.css">
<link rel="stylesheet" href="Alien.css">

Please merge it @YadavAkhileshh

[github-actions]

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[github-actions]

🎉🎉 Thank you for your contribution! Your PR #658 has been merged! 🎉🎉