Fix minor issues with Code Samples

- The description gets deleted if it matches the title exactly (due to
  how our plugin finds the text of the README). Changed a couple
  instances to not match exactly so this doesn't happen.
- Changed the top level of the Code Sampels layout to be a <main>
  element, which allows some styles to apply correctly and also helps
  the search crawler find the contents of the page.

_code-samples/did/README.md

@@ -1,3 +1,3 @@
 # Create, Update, and Delete Decentralized Identifiers (DIDs)
 
-Create, Update, and Delete Decentralized Identifiers (DIDs). A Decentralized Identifier (DID) is a new type of identifier defined by the World Wide Web Consortium (W3C) that enables verifiable, digital identities.
+Create, update, and delete decentralized identifiers (DIDs). A Decentralized Identifier (DID) is a new type of identifier defined by the World Wide Web Consortium (W3C) that enables verifiable, digital identities.

_code-samples/price_oracles/README.md

@@ -1,3 +1,3 @@
 # Create, Update, and Delete Price Oracles
 
-Create, Update, and Delete Price Oracles. A price oracle is a mechanism that feeds external data, such as asset prices, and exchange rates, onto the XRPLedger.
+Create, update, and delete Price Oracles. A price oracle is a mechanism that feeds external data, such as asset prices, and exchange rates, onto the XRPLedger.

resources/code-samples.page.tsx

@@ -29,7 +29,7 @@ export default function CodeSamples() {
   const { codeSamples, langs } = usePageSharedData<any>('code-samples');
 
   return (
-    <div className="landing page-community">
+    <main className="landing page-code-samples">
       <div className="">
         <section className="py-26">
           <div className="col-lg-8 mx-auto text-lg-center">
@@ -126,6 +126,6 @@ export default function CodeSamples() {
           </div>
         </section>
       </div>
-    </div>
+    </main>
   );
 }