docs: add okuna291 as a contributor (#470)

* docs: update README.md

* docs: update .all-contributorsrc

Author: allcontributors[bot]

.all-contributorsrc

@@ -519,6 +519,15 @@
       "contributions": [
         "maintenance"
       ]
+    },
+    {
+      "login": "okuna291",
+      "name": "okuna291",
+      "avatar_url": "https://avatars1.githubusercontent.com/u/5407359?v=4",
+      "profile": "https://github.com/okuna291",
+      "contributions": [
+        "ideas"
+      ]
     }
   ],
   "contributorsPerLine": 7,