triangle: update instructions append (#1934)

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discussion](http://forum.exercism.org/t/pr-to-update-instructions-append-md-for-triangle/11752/6)

exercises/practice/triangle/.docs/instructions.append.md

@@ -13,7 +13,7 @@ Or maybe you will come up with an approach that uses none of those!
 ## Non-integer lengths
 
 The base exercise tests identification of triangles whose sides are all
-integers. However, some triangles cannot be represented by pure integers. A simple example is a triangle with a 90 degree angle between two equal sides of length 1. Its third side has the length square root of 2, which is an irrational number. No integer can represent it.
+integers. However, some triangles cannot be represented by pure integers. A simple example is a triangle with a 90 degree angle between two equal sides of length 1. Its third side has the length square root of 2, which is an irrational number (meaning it cannot be written as an integer or a fraction).
 
 It would be tedious to rewrite the analysis functions to handle both integer and floating-point cases, and particularly tedious to do so for all potential integer and floating point types: given signed and unsigned variants of bitwidths 8, 16, 32, 64, and 128, that would be 10 reimplementations of fundamentally the same code even before considering floats!