Add sitemap.xml for better SEO

A sitemap.xml file has been added to the public directory. This update is intended to enhance Search Engine Optimization (SEO). The sitemap includes URLs for the main site, about page, projects page, resume page, and the contact me page, all with their last modification dates.

public/sitemap.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+    <url>
+        <loc>https://www.roessner.tech</loc>
+        <lastmod>2023-12-05</lastmod>
+    </url>
+    <url>
+        <loc>https://www.roessner.tech/#/about</loc>
+        <lastmod>2023-12-05</lastmod>
+    </url>
+    <url>
+        <loc>https://www.roessner.tech/#/projects</loc>
+        <lastmod>2023-12-05</lastmod>
+    </url>
+    <url>
+        <loc>https://www.roessner.tech/#/resume</loc>
+        <lastmod>2023-12-05</lastmod>
+    </url>
+    <url>
+        <loc>https://www.roessner.tech/#/contactme</loc>
+        <lastmod>2023-12-05</lastmod>
+    </url>
+</urlset>