dominoes: improve description readability (#972)

dominoes: improve description readability

exercises/dominoes/description.md

@@ -5,9 +5,9 @@ correct domino chain (the dots on one half of a stone match the dots on the
 neighbouring half of an adjacent stone) and that dots on the halfs of the stones
 which don't have a neighbour (the first and last stone) match each other.
 
-For example given the stones `21`, `23` and `13` you should compute something
-like `12 23 31` or `32 21 13` or `13 32 21` etc, where the first and last numbers are the same.
+For example given the stones `[2|1]`, `[2|3]` and `[1|3]` you should compute something
+like `[1|2] [2|3] [3|1]` or `[3|2] [2|1] [1|3]` or `[1|3] [3|2] [2|1]` etc, where the first and last numbers are the same.
 
-For stones 12, 41 and 23 the resulting chain is not valid: 41 12 23's first and last numbers are not the same. 4 != 3
+For stones `[1|2]`, `[4|1]` and `[2|3]` the resulting chain is not valid: `[4|1] [1|2] [2|3]`'s first and last numbers are not the same. 4 != 3
 
 Some test cases may use duplicate stones in a chain solution, assume that multiple Domino sets are being used.