Added a bit of documentation regarding frontend testing

Also added shortcut in the Makefile
6 jobs for add_frontend_testing in 4 minutes and 23 seconds (queued for 1 second)
Status Job ID Name Coverage
  Check
passed #452542
docker
check_back

00:00:35

passed #452543
docker
check_front

00:01:05

 
  Test
passed #452544
docker
test_back

00:00:44

89.0%
passed #452545
docker
test_frontend

00:00:53

 
  Lint
passed #452547
docker
eslint

00:00:52

passed #452546
docker
flake8

00:00:12