graph: Clarify wording for GRAPH_USERNAME_MATCH setting

services/graph/pkg/config/config.go

@@ -104,7 +104,7 @@ type Identity struct {
 // API represents API configuration parameters.
 type API struct {
 	GroupMembersPatchLimit int    `yaml:"group_members_patch_limit" env:"GRAPH_GROUP_MEMBERS_PATCH_LIMIT" desc:"The amount of group members allowed to be added with a single patch request."`
-	UsernameMatch          string `yaml:"graph_username_match" env:"GRAPH_USERNAME_MATCH" desc:"Option to allow legacy usernames. Supported options are 'default' and 'none'."`
+	UsernameMatch          string `yaml:"graph_username_match" env:"GRAPH_USERNAME_MATCH" desc:"Apply restrictions to usernames. Supported values are 'default' and 'none'. When set to 'default', user names must not start with a number and are restricted to ASCII characters. When set to 'none', no restrictions are applied. The default value is 'default'."`
 	AssignDefaultUserRole  bool   `yaml:"graph_assign_default_user_role" env:"GRAPH_ASSIGN_DEFAULT_USER_ROLE" desc:"Whether to assign newly created users the default role 'User'. Set this to 'false' if you want to assign roles manually, or if the role assignment should happen at first login. Set this to 'true' (the default) to assign the role 'User' when creating a new user."`
 }