cli: fix minor typo (#23811)

Author: kimshrier

vlib/cli/README.md

@@ -1,7 +1,7 @@
 ## Description
 
 `cli` is a command line option parser, that supports
-declarative subcommands, each having separate set of options.
+declarative subcommands, each having a separate set of options.
 
 See also the `flag` module, for a simpler command line option parser,
 that supports only options.