chore(gnokey): update long help (gnolang#2712)

## Description

This PR updates the `gnokey` long help text.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [x] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gno.land/pkg/keyscli/root.go

@@ -17,7 +17,7 @@ func NewRootCmd(io commands.IO, base client.BaseOptions) *commands.Command {
 	cmd := commands.NewCommand(
 		commands.Metadata{
 			ShortUsage: "<subcommand> [flags] [<arg>...]",
-			LongHelp:   "Manages private keys for the node",
+			LongHelp:   "gno.land keychain & client",
 			Options: []ff.Option{
 				ff.WithConfigFileFlag("config"),
 				ff.WithConfigFileParser(fftoml.Parser),