doc: add missing comma in child_process.md

Adds a comma after "blocks" in a sentence explaining how subprocesses
may pause when the pipe buffer is full. This improves readability and
clarifies the meaning of the sentence, preventing misinterpretation of
"blocks waiting" as a compound phrase.

No functional code is affected.

PR-URL: #58862
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: ronijames008

doc/api/child_process.md

@@ -48,7 +48,7 @@ By default, pipes for `stdin`, `stdout`, and `stderr` are established between
 the parent Node.js process and the spawned subprocess. These pipes have
 limited (and platform-specific) capacity. If the subprocess writes to
 stdout in excess of that limit without the output being captured, the
-subprocess blocks waiting for the pipe buffer to accept more data. This is
+subprocess blocks, waiting for the pipe buffer to accept more data. This is
 identical to the behavior of pipes in the shell. Use the `{ stdio: 'ignore' }`
 option if the output will not be consumed.