Fix link to registration example (#396)

Author: eigenvivek

README.md

@@ -103,7 +103,7 @@ optimization runs like this:
 ![](experiments/registration.gif)
 
 The full example is available at
-[`optimizers.ipynb`](https://vivekg.dev/DiffDRR/tutorials/optimizers.html).
+[`registration.ipynb`](https://vivekg.dev/DiffDRR/tutorials/registration.html).
 
 #### *🆕 Examples on Real-World Data 🆕*
 

notebooks/index.ipynb

@@ -180,7 +180,7 @@
     "![Iterative optimization of moving DRR to a target DRR.](https://cdn.githubraw.com/eigenvivek/DiffDRR/main/experiments/registration.gif)\n",
     "\n",
     "The full example is available at\n",
-    "[`optimizers.ipynb`](https://vivekg.dev/DiffDRR/tutorials/optimizers.html)\n",
+    "[`registration.ipynb`](https://vivekg.dev/DiffDRR/tutorials/registration.html)\n",
     "\n",
     "#### *🆕 Examples on Real-World Data 🆕*\n",
     "\n",