add an example of finding close matches (#1152)

continue discussion on #1149 
Adds subcommand prefix matching as a modifier to CLI.  
Adds an example of close matching logic for further exploration.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

book/chapters/subcommands.md

@@ -105,6 +105,7 @@ at the point the subcommand is created:
 - Fallthrough
 - Group name
 - Max required subcommands
+- prefix_matching
 - validate positional arguments
 - validate optional arguments
 
@@ -156,6 +157,14 @@ ignored, even if they could match. Git is the traditional example for prefix
 commands; if you run git with an unknown subcommand, like "`git thing`", it then
 calls another command called "`git-thing`" with the remaining options intact.
 
+### prefix matching
+
+A modifier is available for subcommand matching,
+`->allow_subcommand_prefix_matching()`. if this is enabled unambiguious prefix
+portions of a subcommand will match. For Example `upgrade_package` would match
+on `upgrade_`, `upg`, `u` as long as no other subcommand would also match. It
+also disallows subcommand names that are full prefixes of another subcommand.
+
 ### Silent subcommands
 
 Subcommands can be modified by using the `silent` option. This will prevent the