README.md: Do some documentation

3 jobs for mastofe/glitch-soc in 13 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #4498
build

00:00:13

 
  Test
skipped #4500
allowed to fail
codequality
skipped #4499
test
 
Name Stage Failure
failed
build Build
Checking out 67e9f93a as mastofe/glitch-soc...
Skipping Git submodules setup
$ # Auto DevOps variables and functions # collapsed multi-line command
$ setup_docker
$ build
Building Dockerfile-based application...
invalid argument "/mastofe-glitch-soc:67e9f93a6ab09142906882661657b548515687b6" for "-t, --tag" flag: invalid reference format
See 'docker build --help'.
ERROR: Job failed: exit code 125