update list/copy cobra short docs to reflect clip default commands

By default, when run without any subcommands or args, `clip` will
execute the `list` command, and when run with 1 arg, `clip` will execute
the `copy` command.

This behavior is already documented in the README, but this should help
make it more obvious to the user how things work when running `clip
help`/`clip --help`.

cmd/copy.go

@@ -37,7 +37,7 @@ import (
 var copyCmd = &cobra.Command{
     Use:   "copy <Clip template>",
     Aliases: []string{"load", "in"},
-    Short: "Copy a Clip template to your clipboard",
+    Short: "Copy a Clip template to your clipboard (default if just running `clip $arg`)",
     Long: `Copy a Clip template to your clipboard`,
     Args: cobra.ExactArgs(1),
     Run: func(cmd *cobra.Command, args []string) {

cmd/list.go

@@ -47,7 +47,7 @@ Example:
   clip list
   clip list --tags-only
   clip list --tags personal,work`,
-    Short: "List available Clip templates/tags",
+    Short: "List available Clip templates/tags (default if just running `clip`)",
     Run: func(cmd *cobra.Command, args []string) {
         list()
     },