add help docs and ?

docs/nodes/Coordinate Pair.md

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+# Coordinate Pair
+
+Combine two COORD values into a single COORDPAIR for use with nodes that accept a line segment or marker pair input.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| a | COORD | Yes | First coordinate (x, y) in fractional [0, 1] units |
+| b | COORD | Yes | Second coordinate (x, y) in fractional [0, 1] units |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| coord_pair | COORDPAIR | Pair of coordinates as a single value |
+
+## Controls
+
+None.
+
+## Limitations
+
+- Coordinates are expected to be in the [0, 1] fractional range; values outside this range may produce unexpected results in downstream nodes.