Fix guide links.

The first link is broken. The second and third links work, but go to the
GitHub view of the relevant file rather than the proper rendered guide.

This commit fixes all three links to point to the rendered guide.

Author: nnethercote

README.md

@@ -7,11 +7,11 @@
   </p>
 
   <h3>
-    <a href="https://rust-gpu.github.io/Rust-CUDA/guide/index.html">Guide</a>
+    <a href="https://rust-gpu.github.io/rust-cuda/index.html">Guide</a>
     <span> | </span>
-    <a href="guide/src/guide/getting_started.md">Getting Started</a>
+    <a href="https://rust-gpu.github.io/rust-cuda/guide/getting_started.html">Getting Started</a>
     <span> | </span>
-    <a href="guide/src/features.md">Features</a>
+    <a href="https://rust-gpu.github.io/rust-cuda/features.html">Features</a>
   </h3>
 <strong>⚠️ The project is still in early development, expect bugs, safety issues, and things that don't work ⚠️</strong>
 </div>