[doc] add dummy documentation for roi selection

3 jobs for fix_5 in 4 minutes and 32 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
passed test:python3.5-stretch-pyqt5 #41884

00:04:32

passed test:python3.5-stretch-pyside2 #41885

00:04:09

passed test:test-xas-tutorials #41886

00:04:13