doc: Fix typo

 * doc/guix.texi (Invoking guix system): Fix typo.

Signed-off-by: Leo Famulari <leo@famulari.name>

doc/guix.texi

@@ -22312,7 +22312,7 @@ switch to it@footnote{This action (and the related actions
 @code{switch-generation} and @code{roll-back}) are usable only on
 systems already running GuixSD.}.
-This effects all the configuration specified in @var{file}: user
+This affects all the configuration specified in @var{file}: user
 accounts, system services, global package list, setuid programs, etc.
 The command starts system services specified in @var{file} that are not
 currently running; if a service is currently running this command will