Updated OVERVIEW.dm to account for Bridge protocol changes

packages/react-devtools/OVERVIEW.md

@@ -54,7 +54,9 @@ Adding a root to the tree requires sending 5 numbers:
 1. add operation constant (`1`)
 1. fiber id
 1. element type constant (`11 === ElementTypeRoot`)
-1. profiling supported flag
+1. root has `StrictMode` enabled
+1. supports profiling flag
+1. supports `StrictMode` flag
 1. owner metadata flag
 
 For example, adding a root fiber with an id of 1:
@@ -178,6 +180,20 @@ Special case of unmounting an entire root (include its descendants). This specia
 
 This operation has no additional payload because renderer and root ids are already sent at the beginning of every operations payload.
 
+#### Setting the mode for a subtree
+
+This message specifies that a subtree operates under a specific mode (e.g. `StrictMode`).
+
+```js
+[
+  7,   // set subtree mode
+  1,   // subtree root fiber id
+  0b01 // mode bitmask
+]
+```
+
+Modes are constant meaning that the modes a subtree mounts with will never change.
+
 ## Reconstructing the tree
 
 The frontend stores its information about the tree in a map of id to objects with the following keys: