Update walletcli usage message and bump version to v0.5.1

- cmd/walletcli/main.go
  - Fixed usage message to correctly escape double quotes around the NWC connection URL.

- pkg/version/version
  - Updated version from v0.5.0 to v0.5.1.

cmd/walletcli/main.go

@@ -12,7 +12,7 @@ import (
 )
 
 func printUsage() {
-	fmt.Println("Usage: walletcli '<NWC connection URL>' <method> [<args...>]")
+	fmt.Println("Usage: walletcli \"<NWC connection URL>\" <method> [<args...>]")
 	fmt.Println("\nAvailable methods:")
 	fmt.Println("  get_wallet_service_info - Get wallet service information")
 	fmt.Println("  get_info                - Get wallet information")

pkg/version/version

@@ -1 +1 @@
-v0.5.0
+v0.5.1