Add Dominoes exercise for Elixir track

elixir/dominoes/.exercism/config.json

@@ -0,0 +1,24 @@
+{
+  "authors": [
+    "Tuxified"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "devonestes",
+    "neenjaw",
+    "sotojuan"
+  ],
+  "files": {
+    "solution": [
+      "lib/dominoes.ex"
+    ],
+    "test": [
+      "test/dominoes_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Make a chain of dominoes."
+}

elixir/dominoes/.exercism/metadata.json

@@ -0,0 +1 @@
+{"track":"elixir","exercise":"dominoes","id":"c3029f8eea4743b88999e49c85863daa","url":"https://exercism.org/tracks/elixir/exercises/dominoes","handle":"negrienko","is_requester":true,"auto_approve":false}