doc: update devcontainer.json and add documentation #413

Job	Run time
Build slim tarball	1m 25s
aarch64-darwin: with shared libraries	8m 14s
x86_64-darwin: with shared libraries	8m 27s
aarch64-linux: with shared libraries	8m 12s
x86_64-linux: with shared libraries	8m 15s
	34m 33s

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