Harmonize the way we link our folders in READMEs

While looking at https://github.com/eclipse/thingweb.node-wot/pull/799 I noticed that we do not have a consistent way of linking our _own_ folders in the repo.

see for example the [main readme](https://github.com/eclipse/thingweb.node-wot/blob/master/README.md).

We use
`https://github.com/eclipse/thingweb.node-wot/blob/master/...`
vs.
`https://github.com/eclipse/thingweb.node-wot/tree/master/...`

Honestly, I do not fully understand the differences/advantages between `blob` and `tree` even after reading some [explanation](https://www.tutorialspoint.com/explain-blob-object-and-tree-object-in-git) ...
Does anyone know what would be the better choice?

PPS: I would like to have a way of pointing to the *current* "master" branch. Meaning that if we once change from `master` to `main` we wouldn't need to change all links in the READMEs.