Created LedSegment enum (markdown)

LedSegment-enum.md

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+The LedSegment represents a readable index into the segments on a SevenSegDigit object.  The names follow the standard naming practices for seven segment displays.  
+
+```
+enum LedSegment
+{
+    LedSegment_A,
+    LedSegment_B,
+    LedSegment_C,
+    LedSegment_D,
+    LedSegment_E,
+    LedSegment_F,
+    LedSegment_G,
+    LedSegment_Decimal, // maybe jumpered to alternate custom segment
+    LedSegment_Custom, // generally not used but maybe connected to a custom segment
+    LedSegment_COUNT
+};
+```