QProcess/Doc: clarify that early crashes happen after started()

This is notable when dynamic linking fails, because that happens before
the first line of main() (or equivalent) of the child process, so even
banners printed by that function may be missing.

Pick-to: 6.7
Change-Id: I5201966b308e48989c06fffd17aa9837156e23f4
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

src/corelib/io/qprocess.cpp

@@ -2193,6 +2193,12 @@ QByteArray QProcess::readAllStandardError()
     printed at the console, and the existing process will continue running
     unaffected.
 
+    \note Success at starting the child process only implies the operating
+    system has successfully created the process and assigned the resources
+    every process has, such as its process ID. The child process may crash or
+    otherwise fail very early and thus not produce its expected output. On most
+    operating systems, this may include dynamic linking errors.
+
     \sa processId(), started(), waitForStarted(), setNativeArguments()
 */
 void QProcess::start(const QString &program, const QStringList &arguments, OpenMode mode)