Add game-of-life input format documentation (#275)

Author: keiravillekode

exercises/practice/game-of-life/.docs/instructions.append.md

@@ -0,0 +1,23 @@
+# Instructions append
+
+## Input/Output format
+
+Each row of the grid is represented as a 64 bit integer.
+
+For example,
+
+```
+    0 1 0
+    1 0 0
+    1 1 0
+```
+
+is represented as
+
+```
+0b010
+0b100
+0b110
+```
+
+The grid has at most 64 columns.