docs: add details in CONTRIBUTING.md #2798

Job	Run time
Coding style	48s
Build docs	45s
Spellcheck / Run spell check	10s
Fast builds / Fast builds (windows-latest, OFF, ON, OFF)	1s
Fast builds / Fast builds (windows-latest, OFF, OFF, OFF)	1s
Fast builds / Fast builds (ubuntu-latest, ON, ON, -DCMAKE_BUILD_TYPE=Release -DUMF_BUILD_BENCHMARKS=ON -DUMF_BU...	42s
Fast builds / Fast builds (ubuntu-latest, OFF, OFF, -DCMAKE_BUILD_TYPE=Release -DUMF_BUILD_BENCHMARKS=ON, OFF)	1m 3s
Fast builds / Fast builds (ubuntu-latest, OFF, ON, -DCMAKE_BUILD_TYPE=Release, ON)	2m 7s
Fast builds / Fast builds (ubuntu-20.04, OFF, ON, -DCMAKE_BUILD_TYPE=Release, ON)	1s
Sanitizers	1s
Qemu	1s
Basic builds	1s
GPU	1s
Benchmarks	1s
MultiNuma	1s
ProxyLib	1s
Valgrind	1s
	5m 46s

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