README : be more explicit about <KIND> and add small example

[sucrecacao]

Hi,
I have been advised to use kak-tree for a plugin I'm working on. But I have trouble getting started with it.
What are the value I can use in the variable ?
Could it be possible to have a tiny example of a basic workflow ? For example how to use kak-tree in a plugin script ?

[ul]

KIND is a placeholder for a node kind. Unfortunately, each parser defines its own set of kinds (that's why I added support for groups into kak-tree so users can unify those kinds).

Imagine your plugin wants to select up to a function scope and you know that parser for this language defines corresponding node kind as fn or you know that user has a group fn defined in their config which abstracts parsers' kinds. Then your plugin script can evaluate command tree-select-parent-node fn to select such scope.

[sucrecacao]

Where can one find the list of all the KIND ?

[ul]

Each parser provides their own. For example, C parser has those: https://github.com/tree-sitter/tree-sitter-c/blob/master/src/node-types.json