[newlib-cygwin] Cygwin: Slightly improve error_start documentation

[Jon TURNEY]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=f2a285bd4f424f0c84017b6051dcdd8acf221de8

commit f2a285bd4f424f0c84017b6051dcdd8acf221de8
Author: Jon Turney <jon.turney@dronecode.org.uk>
Date:   Wed Jun 10 14:52:41 2020 +0100

    Cygwin: Slightly improve error_start documentation

Diff:
---
 winsup/doc/cygwinenv.xml | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/winsup/doc/cygwinenv.xml b/winsup/doc/cygwinenv.xml
index f549fee0d..a52b6ac19 100644
--- a/winsup/doc/cygwinenv.xml
+++ b/winsup/doc/cygwinenv.xml
@@ -28,9 +28,13 @@ Defaults to off.</para>
 which is useful for debugging.  <filename>Win32filepath</filename> is
 usually set to the path to <command>gdb</command> or
 <command>dumper</command>, for example
-<filename>C:\cygwin\bin\gdb.exe</filename>. 
+<filename>C:\cygwin\bin\gdb.exe</filename>.
 There is no default set.
 </para>
+<para>
+The filename of the executing program and it's Windows process id are appended
+to the command as arguments.
+</para>
 </listitem>
 
 <listitem>