man: update 'runc update --pids-limit' text

Signed-off-by: Aleksa Sarai <[email protected]>

Author: cyphar

man/runc-update.8.md

@@ -85,7 +85,8 @@ stdin. If this option is used, all other options are ignored.
 (i.e. use unlimited swap).
 
 **--pids-limit** _num_
-: Set the maximum number of processes allowed in the container.
+: Set the maximum number of processes allowed in the container. Use **-1** to
+unset the limit.
 
 **--l3-cache-schema** _value_
 : Set the value for Intel RDT/CAT L3 cache schema.