docs: add gauthier-th as a contributor for code (#766)

* docs: update README.md [skip ci]

* docs: update .all-contributorsrc [skip ci]

---------

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

.all-contributorsrc

@@ -331,6 +331,15 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "gauthier-th",
+      "name": "Gauthier",
+      "avatar_url": "https://avatars.githubusercontent.com/u/37781713?v=4",
+      "profile": "https://gauthierth.fr/",
+      "contributions": [
+        "code"
+      ]
     }
   ]
 }