gst-launch: Update man page

Add description for newly add "position" option
22 jobs for launch-pos in 106 minutes and 22 seconds (queued for 10 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #480511
gst indent

00:00:37

passed #480510
manifest

00:00:55

 
  Build
passed #480517
build cerbero android universal

00:11:16

passed #480518
build cerbero cross win32

00:11:55

passed #480519
build cerbero cross win64

00:09:22

passed #480516
build cerbero fedora x86_64

00:05:54

manual #480521
gst-ios-12.2 allowed to fail manual
build cerbero ios universal
passed #480520
gst-macos-10.14
build cerbero macos x86_64

00:10:55

passed #480512
build fedora x86_64

00:06:42

passed #480513
build nodebug fedora x86_64

00:05:57

passed #480514
build static fedora x86_64

00:16:52

passed #480515
build static nodebug fedora x86_64

00:11:32

 
  Test
passed #480522
check fedora

00:03:56

passed #480523
integration testsuites fedora

00:19:40

passed #480528
valgrind bad

00:11:03

passed #480525
valgrind base

00:08:20

passed #480524
valgrind core

00:13:49

passed #480529
valgrind ges

00:11:01

passed #480526
valgrind good

00:13:17

passed #480527
valgrind ugly

00:02:40

 
  Integrate
passed #480530
android universal examples

00:10:09

passed #480531
documentation

00:04:30