doc: '--inherit' option can be repeated.

* doc/guix.texi (Invoking guix environment): Mention that '--inherit'
can be repeated.

doc/guix.texi

@@ -4462,7 +4462,8 @@ creating an environment in which search paths only contain package inputs.
 @item --inherit=@var{regexp}
 When used alongside @option{--pure}, inherit all the environment variables
 matching @var{regexp}---in other words, put them on a ``white list'' of
-environment variables that must be preserved.
+environment variables that must be preserved.  This option can be repeated
+several times.
 
 @example
 guix environment --pure --inherit=^SLURM --ad-hoc openmpi @dots{} \