Add custom template section to the documentation

[caroso1222]

Sorry if I'm missing something, I just think we should add a section in the documentation which explains how to set a custom template for the nodes. I had to look in the code to figure out that I had to include the template as a transcluded content inside the tree component:

<tree [tree]="propsTree">
  <ng-template let-node>
    <b>{{node.value}}</b>
  </ng-template>
</tree>

I'm up to the task of opening a PR for this, but I better double check and ask if this is the recommended approach to set custom content for a node.

Cheers!

[rychkog]

@caroso1222 Good point! Looking forward to your PR.