📝 Added a comment with further explanation for rounding (#357)

* Added a comment with further explanation for rounding

* Added changes requested by @vexx32

PSKoans/Koans/Introduction/AboutNumbers.Koans.ps1

@@ -61,6 +61,13 @@ Describe 'Basic Number Types' {
 Describe "Banker's Rounding" {
 
     It 'rounds to nearest even number on .5' {
+        <#
+            The rounding used in PowerShell is called "Rounding to Even" or "Banker's Rounding".
+            Numbers will be rounded to the nearest _even_ Integer.
+
+            This behaviour stems from the underlying library method [math]::Round() which is documented in more detail here:
+            https://docs.microsoft.com/en-us/dotnet/api/system.math.round#midpoint-values-and-rounding-conventions
+        #>
 
         # Try and guess how PowerShell will round these numbers
         ____ | Should -Be ([int]2.5)