docs(web): explain the Japanese name + yui reciprocity on About

docs/what-is-tane.md

@@ -53,10 +53,19 @@ still do it with notebooks and spreadsheets.
 Seed groups and networks, gardens and collectives, growers… and anyone with a few packets
 put away. For all ages, from 10 to 80.
 
-## The name
+## A Japanese name
 
-**Tane** means "seed" (種). It comes from *tanemaki* (種まき), "to sow seeds" in Japanese, a
-nod to old customs of mutual aid between neighbours (sharing the work, saving together).
+**Tane** means "seed" (種); *tanemaki* (種まき) means "to sow seeds". And it's no accident
+that the name is Japanese. In much of rural Japan, farming life rested on mutual aid —
+*yui* (結): neighbours lent one another their labour, and their seed and rice too. Whoever
+received grain or seed in a hard year gave it back after the harvest — a little of the
+much that seed had multiplied. That way the common stock never ran dry: every loan, once
+grown, gave back more than it took.
+
+That very idea is the heart of Tane. When you share seeds you can attach a **Plantare**: a
+promise to return, when you can, a similar amount of free seed. It isn't a debt — it's a
+pledge to keep the seed alive and moving. And because returning it means growing it, and
+growing multiplies it, every loan makes the commons grow instead of shrinking it.
 
 ## Where it stands and how to help