updating the informations needed when adding a root node to a tree in react-devtools overview doc

[IDrissAitHafid]

Summary

1. Updated the value of ElementTypeRoot to 11, as it is here:
   

   react/packages/react-devtools-shared/src/types.js

   Line 32 in 3cc5645

   export const ElementTypeRoot = 11;

2. Added a fifth number required when adding a root node to a tree, as I found and understand from this line:
   

   react/packages/react-devtools-shared/src/backend/renderer.js

   Line 1142 in 50d9451

   pushOperation(hasOwnerMetadata ? 1 : 0);

   
   and from this one:
   

   react/packages/react-devtools-shared/src/devtools/store.js

   Line 763 in 30b4710

   const hasOwnerMetadata = operations[i] > 0;

cc @bvaughn

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[IDrissAitHafid]

Question: shouldn't this line be deleted from the example of adding a leaf node?
3, // encoded display name size
`
At least that's what I understood from reading the code, but this phrase confused me:

Adding a leaf node takes a variable number of numbers

So, I just wanted to ask for your confirmation before opening a PR 😅.

[bvaughn]

I have not made much of an effort to keep the OVERVIEW doc up to date as DevTools has changed over time. I think it's worth doing, it's just something I haven't had/taken/made time for.

WRT the "encoded display name size" – we used to send encoded strings inline, so that position carried the size of the string and then the next N numbers were the actual encoded string. At some point, we migrated things to use a string table and so now we just send an ID. That means the overall number of elements is fixed now, where as it used to be variable. Looks like the attempt to update the OVERVIEW after this change was flubbed a bit.

So the "encoded display name size" line could be deleted and the "variable number" comment could be updated.

[IDrissAitHafid]

Thanks for the clarification.
Anyway, the code itself is well documented and it's just another chance to contribute 😄