add m_translation doc

docs/lib-m_translation.md

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+# m_translation
+
+Generate a 4x4 transformation matrix which can pass into `multmatrix` to translates (moves) its child elements along the specified vector.
+
+## Parameters
+
+- `v` : The normal vector of a plane intersecting the origin through which to mirror the object.
+
+## Examples
+
+	include <m_translation.scad>;
+
+	cube(2, center = true); 
+	multmatrix(m_translation([5, 0, 0]))
+	sphere(1,center = true);
+
+![m_translation](images/lib-m_translation-1.JPG)
+