Clarify inline action vs regsitry based trigger gotcha

In most cases, defining actions under `$jason.head.actions` and calling them via `trigger` is recommended.

This is because if we ever happen to pass around dynamic arguments, these template expressions may get instantiated on view render and will baked into the view.

For example, in the following case we want to display an alert with the local variable `val` at the time of user tap.

```
{
"type": "label",
"text": "push",
"action": {
"type": "$util.alert",
"options": {
"title": "value",
"description": "{{$get.val}}"
}
}
}
```

However what actually happens is: this will get rendered at load time **with the `val` value at the time of render**. Then this action is not dynamic anymore because all its arguments have been instantiated. This is why it's recommended that you put all actions under `head.actions` so that these don't get instantiated at view render.

But this point can be confusing for people new to the framework.

So this issue is for figuring out how to deal with this problem. Could be through better documentation, could be through some sort of warning messages, something else, or all of the above.

Start with the inline action example using `$jason.head.actions`, `trigger`, and `{{$get.val}}`; the issue provides no repository files or tests to inspect. Done means establishing and documenting how render-time and tap-time arguments should behave, or defining another concrete way to prevent newcomers from confusing the two.

Written by the indexing model from the issue text.