docs: correct meaning of DesktopCapturerSource.id (#27255)

* docs: correction meaning of DesktopCapturerSource.id

Corrected the meaning of the id string to match observed behavior
(verified on Windows 10 and Ubuntu).

* chore: adjust wordings

Co-authored-by: Cheng Zhao <[email protected]>

docs/api/structures/desktop-capturer-source.md

@@ -3,7 +3,10 @@
 * `id` String - The identifier of a window or screen that can be used as a
   `chromeMediaSourceId` constraint when calling
   [`navigator.webkitGetUserMedia`]. The format of the identifier will be
-  `window:XX` or `screen:XX`, where `XX` is a random generated number.
+  `window:XX:YY` or `screen:ZZ:0`. XX is the windowID/handle. YY is 1 for
+  the current process, and 0 for all others. ZZ is a sequential number
+  that represents the screen, and it does not equal to the index in the
+  source's name.
 * `name` String - A screen source will be named either `Entire Screen` or
   `Screen <index>`, while the name of a window source will match the window
   title.