Add acronym AFK (#127)

Author: yusha-g

data/acronyms.json

@@ -17,6 +17,12 @@
     "Usage": "AFAIK, he will be away for three months.",
     "Example": "<a href=\"https://github.com/d-edge/Diffract/issues/1#issuecomment-946781621\">Diffract</a>"
   },
+  {
+    "Abbreviation": "AFK",
+    "Definition": "Away From Keyboard",
+    "Usage": "I'm going afk, dinner's ready.",
+    "Example": "<a href=\"https://dictionary.cambridge.org/dictionary/english/afk\">Cambridge Dictionary</a>"
+  },
   {
     "Abbreviation": "AOA",
     "Definition": "Analysis of Alternatives",