docs: relative_point_origin added to the absolute quantities blog post

docs/blog/posts/introducing-absolute-quantities.md

@@ -135,9 +135,13 @@ will not need any specifier to denote them.
 For example:
 
 ```cpp
-quantity<point<isq::mass>> m1(10 * kg);   // point quantity with an implicit point origin
-quantity<isq::mass>        m2 = 15 * kg;  // absolute quantity (e.g., non-negative)
-quantity<delta<isq::mass>> m3 = m1 - m2;  // delta quantity (e.g., may be negative)
+inline constexpr struct tare final : relative_point_origin<quantity_point{2 * kg}> {} tare;
+
+quantity<point<isq::mass>> m1(10 * kg);          // point quantity with an implicit point origin
+quantity<point<isq::mass>> m2 = tare + 8 * kg;   // point quantity with an explicit relative point origin
+quantity<isq::mass>        m3 = 15 * kg;         // absolute quantity (e.g., non-negative)
+quantity<delta<isq::mass>> m13 = m1 - m3;        // delta quantity (e.g., may be negative)
+quantity<delta<isq::mass>> m23 = m2 - m3;        // delta quantity (e.g., may be negative)
 ```
 
 With the above, the previous examples may be refactored to: