dev/releases/README.md: update & expand (#5743) #5470

Job	Run time
Cross compiler for s390x	27m 15s
Test in OpenBSD	8m 24s
testinstall - - ubuntu-latest	4m 45s
teststandard - - ubuntu-latest	18m 49s
testmanuals - - ubuntu-latest	5m 56s
testexpect testmockpkg testspecial test-compile testlibgap testkernel testworkspace - - ubuntu-latest	6m 40s
testpackages testinstall-loadall - - ubuntu-latest	26m 2s
makemanuals testmakeinstall - CONFIGFLAGS="--prefix=/tmp/gapprefix" NO_COVERAGE=1 - ubuntu-latest	5m 23s
teststandard - ABI=32 CONFIGFLAGS="" - ubuntu-20.04	18m 4s
testinstall - HPCGAP=yes ABI=64 - ubuntu-latest	7m 6s
testmockpkg testinstall - BOOTSTRAP_MINIMAL=yes - macos-latest	3m 42s
testbugfix - CONFIGFLAGS="--enable-memory-checking" - ubuntu-latest	27m 41s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=64 BUILDDIR=out-of-tree CONFIGFLAGS="--enable-valgrind" - ubuntu-latest	3m 41s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=32 BUILDDIR=out-of-tree CONFIGFLAGS="" - ubuntu-20.04	3m 33s
testinstall - JULIA=yes CONFIGFLAGS="--enable-debug --disable-Werror" - ubuntu-20.04	4m 14s
testmockpkg testinstall - - windows-2019	15m 35s
Send Slack notification on status change	5s
	3h 6m 55s

Provide feedback