docs: Clarify meaning of "list" and "cond" for "if" and "while" commands respectively

docs: Clarify meaning of "list" and "cond" for "if" and "while" commands respectively

It is not clear from the documentation what a "list" is in the context
of the "if" command. Note that its a list of simple commands separated
by a ";" and that only the exit status of the last command matters.
The same is true for the "cond" parameter to the "while" command.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>