Update page title and description of Technical Changelog (#715)

The PR updates the page title and description of the technical changelog
page.

Author: MaedahBatool

docs/technical-changelog.mdx

@@ -1,6 +1,6 @@
-# Changelog
+# Technical Changelog
 
-All notable changes to Sourcegraph are documented in this file.
+This page documents all notable changes to Sourcegraph. For more detailed changelog posts, please [read here](https://sourcegraph.com/changelog/). 
 
 {/* CHANGELOG_START */}