qspawn: describe where `$rpipe' come from

It wasn't immediately obvious to me after several months of
not looking at this code.

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index 9aede103..943ee801 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -122,7 +122,7 @@ sub psgi_qx {
                 eval { $qx_cb->($qx) };
                 $qx = undef;
         };
-        my $rpipe;
+        my $rpipe; # comes from popen_rd
         my $async = $env->{'pi-httpd.async'};
         my $cb = sub {
                 my $r = sysread($rpipe, my $buf, 8192);
@@ -137,7 +137,7 @@ sub psgi_qx {
         };
         $limiter ||= $def_limiter ||= PublicInbox::Qspawn::Limiter->new(32);
         $self->start($limiter, sub { # may run later, much later...
-                ($rpipe) = @_;
+                ($rpipe) = @_; # popen_rd result
                 if ($async) {
                 # PublicInbox::HTTPD::Async->new($rpipe, $cb, $end)
                         $async = $async->($rpipe, $cb, $end);