feat(wiktionary): add Wiktionary extension.

Author: luleyleo

extensions/wiktionary/README.md

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+# Wiktionary
+
+An unofficial [Wiktionary](https://www.wiktionary.org) extension for Vicinae.
+
+## Features
+
+Implemented:
+- Search word definitions
+
+Missing:
+- Search selected words
+- Search etymology
+- Search Synonyms
+
+## Thanks
+
+This is based on the [raycast-wiktionary](https://github.com/adielbm/raycast-wiktionary#) extension by [adielbm](https://github.com/adielbm).