Triangle: explicitly exclude degenerate triangles (#2579)

* Triangle: explicitly exclude degenerate triangles

* Update exercises/triangle/description.md

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Co-authored-by: Jeremy Walker <[email protected]>

Author: IsaacG

exercises/triangle/description.md

@@ -13,6 +13,11 @@ A _scalene_ triangle has all sides of different lengths.
 
 For a shape to be a triangle at all, all sides have to be of length > 0, and the sum of the lengths of any two sides must be greater than or equal to the length of the third side.
 
+~~~~exercism/note
+We opted to not include tests for degenerate triangles (triangles that violate these rules) to keep things simpler.
+You may handle those situations if you wish to do so, or safely ignore them.
+~~~~
+
 In equations:
 
 Let `a`, `b`, and `c` be sides of the triangle.