add source for words_alpha.txt

notebooks/generate_anagrams.ipynb

@@ -42,6 +42,7 @@
     }
    ],
    "source": [
+    "# The file `words_alpha.txt` has been obtained from https://github.com/dwyl/english-words \n",
     "with open(\"./reasoning_gym/data/words_alpha.txt\") as f:\n",
     "    words = f.read().splitlines()\n",
     "print(len(words))"