Add meta description (#1020)

Added a meta description tag to the HTML head to improve SEO and ensure
proper display in search engine results.

## High Level Overview of Change

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### Context of Change

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### Type of Change

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- [ x] Bug fix (non-breaking change which fixes an issue)

### TypeScript/Hooks Update

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- [ ] Updated files to React Hooks
- [ ] Updated files to TypeScript

## Before / After

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src/index.html

@@ -8,6 +8,7 @@
   <meta name="apple-mobile-web-app-capable" content="yes">
   <meta name="mobile-web-app-capable" content="yes">
   <meta name="google-site-verification" content="k8jb6KQfitguHqeR97svoRnnsgzvs3a0FliHbESVDk4" />
+  <meta name="description" content="Discover the XRP Ledger with this open source explorer. Check account balances, transactions, validators, nodes and analyze blockchain activity.">
   <!--
       manifest.json provides metadata used when your web app is added to the
       homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/