Add crypttab.5 manpage

[sh1r4s3]

No description provided.

[leahneukirchen]

This seems to be copied without attribution from some other project?

Also, manpages should preferably written in mdoc...

[sh1r4s3]

@leahneukirchen This one I wrote mostly myself I used fstab(5) as example. Some of the options text I used from cryptsetup-open(8). Also two first lines of examples I took from Arch Linux manpage.

[vincele]

related issue:
#39

[dkwo]

The /etc/crypttab file can in principle be consumed by the init (e.g. runit-void) but also by the initram generator (e.g. dracut).
In my understanding, in the first case we are dealing with non-root filesystems only (since / has already been decrypted and mounted by the initram at this point, see also the line # NOTE: Do not list your root (/) partition here. in our crypttab). In the second case, we are dealing with how to decrypt the root file system in the initram, see e.g. the example in the docs https://docs.voidlinux.org/installation/guides/fde.html#luks-key-setup
If this is correct, should the manpage of crypttab (hence initram and init dependent, unlike fstab) mention both cases? It may be useful to look at Debian's man page of crypttab for inspiration, in particular https://manpages.debian.org/bookworm/cryptsetup/crypttab.5.en.html#ON_DIFFERENT_CRYPTTAB_FORMATS