terminal-colors.d: (man) re-apply improvements lost in merge

terminal-colors.d: (man) re-apply improvements lost in merge

Commit 3252142521 improved the man page formatting and wording,
but merge commit d708fc7db6 undid all those changes due to a
conflict resolution mess.  Re-apply the improvements:

 - do not show 'type' as an optional part in the synopsis
 - indent the list of file types for clarity
 - correct and improve several wordings
 - fix grammar ("which provide" not "which provides")
 - compact the examples section

Addresses: https://github.com/util-linux/util-linux/commit/3252142521
Signed-off-by: Karel Zak <kzak@redhat.com>