Document new feature: CRIU/autofs: support "browse" autofs config option

>Description of problem:
Autofs map that is browsable after suspend/resume
no longer lists its keys

>How reproducible:
2/2

>Steps to Reproduce:
1. Prepare browsable map (using autofs package):
CT-400 /# cat /etc/auto.master.d/stuff.autofs
/stuff /etc/auto.stuff browse
CT-400 /#
CT-400 /# cat /etc/auto.stuff
d1 -fstype=tmpfs tmpfs
d2 -fstype=tmpfs tmpfs

CT-400 /#

Check contents:

CT-400 /# grep stuff /proc/mounts
/etc/auto.stuff /stuff autofs rw,relatime,fd=19,pipe_ino=113504,pgrp=362,timeout=300,minproto=5,maxproto=5,indirect 0 0
CT-400 /#
CT-400 /# ls /stuff
d1 d2
CT-400 /#

2. Make suspend/resume

3. Check contents again:

CT-400 /# ls /stuff
CT-400 /#

>Actual results:
After suspend/resume, map keys are not listed

>Expected results:
map keys are listed (as before)

>Host OS:
[root@s112 ~]# cat /etc/parallels-release
Virtuozzo release 7.0.0 (3443)
[root@s112 ~]# uname -a
Linux s112.qa.sw.ru 3.10.0-327.18.2.vz7.14.14 #1 SMP Thu Jun 9 12:27:02 MSK 2016 x86_64 x86_64 x86_64 GNU/Linux
[root@s112 ~]# rpm -q criu
criu-2.1.0.36-1.vz7.x86_64
[root@s112 ~]#


>Guest OS:
centos-7-x86_64

>Report URL:
http://reports.parallels.com/Reports/Report.aspx?ReportId=103553706

>Additional info: