Clarify where the shell-command output goes

* lisp/simple.el (shell-command):
* doc/emacs/misc.texi (Single Shell): Clarify where the output
goes if the specified buffer isn't the current one (bug#40896).
10 jobs for master in 415 minutes (queued for 7 seconds)
Status Job ID Name Coverage
  Build Images
passed #38730
build-image-inotify

02:39:21

 
  Normal
failed #38731
test-all-inotify

00:29:35

 
  Platform Images
passed #38732
build-image-filenotify-gio

02:41:30

passed #38733
build-image-gnustep

00:54:19

 
  Platforms
passed #38734
test-filenotify-gio

00:17:43

passed #38735
test-gnustep

00:04:45

 
  Native Comp Images
passed #38736
build-native-comp-speed0

06:16:29

passed #38737
build-native-comp-speed1

04:37:43

passed #38738
build-native-comp-speed2

04:37:13

 
  Native Comp
failed #38739
test-native-comp-speed0

00:38:28

 
Name Stage Failure
failed
test-native-comp-speed0 Native Comp
Uploading artifacts for failed job
Uploading artifacts...
test-native-comp-speed0-87c23670/: found 426 matching files and directories

Uploading artifacts as "archive" to coordinator... ok
id=38739 responseStatus=201 Created token=WwuPpCM3
Uploading artifacts...
test-native-comp-speed0-87c23670/junit-test-report.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... ok
id=38739 responseStatus=201 Created token=WwuPpCM3
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 2

failed
test-all-inotify Normal
$ find ${test_name} -type d -depth -exec rmdir {} + 2>/dev/null
Uploading artifacts for failed job
Uploading artifacts...
test-all-inotify-87c23670/: found 426 matching files and directories

Uploading artifacts as "archive" to coordinator... ok
id=38731 responseStatus=201 Created token=8xjHX5_u
Uploading artifacts...
test-all-inotify-87c23670/junit-test-report.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... ok
id=38731 responseStatus=201 Created token=8xjHX5_u
Cleaning up file based variables
ERROR: Job failed: exit code 2