Add some useful doc comments about node ids

[StratusFearMe21]

Hi! I'm currently using tree-sitter to power a plain-text presentation program I'm making, which has a Language Server integration. As a user is editing, I tried to associate slides with the Node IDs they corresponded to, that way I could easily update a slideshow preview on every keystroke

---------------- node id
{
    Title: ViewBox[0]^^..,
    Subtitle: ViewBox[1]__..,
}[]
----------------

---------------- node id
{
    Title: ViewBox[0]^^|,
    Subtitle: ViewBox[1]__|,
    NewText: Size[0]__..,
}[]
----------------

I found that this didn't work as expected, but it did work when I took the Node ID of a specific token within each slide, in my case, the first bracket

---------------- node id
{
----------------
    Title: ViewBox[0]^^..,
    Subtitle: ViewBox[1]__..,
}[]

---------------- node id
{
----------------
    Title: ViewBox[0]^^|,
    Subtitle: ViewBox[1]__|,
    NewText: Size[0]__..,
}[]

I was under the impression that if a Node was not marked as having changed, that it would always be reused. I found that this was not the case, and added some doc comments to the id() function under the Node struct. If there's anywhere else this information should go, I'll update this PR and put it there too. tree-sitter has been such an amazing tool to use, and integrate into everything I'm doing, and I can't thank y'all enough for making it 😄

[StratusFearMe21]

Sorry, old commits got in the PR, one sec Fixed