Add context to comment on php-fpm log-output

See #358 (comment).

Author: jaylinski

8.0/alpine3.16/fpm/Dockerfile

@@ -467,7 +467,8 @@ RUN set -eux; \
 		echo; echo '; https://github.com/docker-library/php/pull/725#issuecomment-443540114'; echo 'log_limit = 8192'; \
 		echo; \
 		echo '[www]'; \
-		echo '; if we send this to /proc/self/fd/1, it never appears'; \
+		echo '; php-fpm closes STDOUT on startup, so sending logs to /proc/self/fd/1 does not work.'; \
+		echo '; https://bugs.php.net/bug.php?id=73886'; \
 		echo 'access.log = /proc/self/fd/2'; \
 		echo; \
 		echo 'clear_env = no'; \