[doc] a-text.md, raycasting

[andreasplesch]

Description:
address raycasting
Changes proposed:

• add a limitations sections with a short explanation.

[dmarcos]

We have a cursor example (https://github.com/aframevr/aframe/blob/master/examples/test/cursor/index.html). Do we add some text there to illustrate how to do it?

[machenmusik]

I think the a-plane labeled with text in https://github.com/aframevr/aframe/blob/master/examples/test/text/scenarios.html would work with cursor, right? If so, maybe we can point at something like that as example.

[ngokevin]

I would rephrase like, to interact with the text via raycaster or cursor, we will need to add a geometry like a plane to the text

[machenmusik]

Yeah, IMO the core text component should be thought of more as a specific type of material / decoration and so to be interacted with, the entity needs a geometry (e.g. plane or box) that defines its area / volume for interaction...?

[andreasplesch]

A simplistic example on the page may suffice ?

<a-text value="Hello, World!"></a-text>

<!-- for cursor detection add geometry -->

<a-text value="click me!" geometry="primitive:plane"></a-text>

[andreasplesch]

The wording is friendlier now although I think it is preferable to say explicitly that text itself does not work with cursor or raycaster to avoid any confusion.

[ngokevin]

I'd add this example below to the limitations, and then:

<a-text value="Now interactable" geometry="primitive: plane"</a-text>

[andreasplesch]

Good idea. Not sure if interactable is a proper word but it is better than interactive.