chore: update /doc.go (gnolang#1964)

- update copyright, license
- add ascii banner (for `go doc`, and `godoc`)

Signed-off-by: moul <94029+moul@users.noreply.github.com>

doc.go

@@ -1,5 +1,5 @@
-// Copyright 2022 Jae Kwon. All rights reserved.
-// SPDX-License-Identifier: GNO License Version 1.0
+// Copyright 2022-2024 NewTendermint, LLC. All rights reserved.
+// SPDX-License-Identifier: Gno Network Public License 3.0
 
 // At first, there was Bitcoin, out of entropy soup of the greater All.
 // Then, there was Ethereum, which was created in the likeness of Bitcoin,
@@ -8,4 +8,10 @@
 // Among these were Tendermint and Cosmos to engineer robust PoS and IBC.
 // Then came Gno upon Cosmos and there spring forth Gnoland,
 // simulated by the Gnomes of the Greater Resistance.
-package readme // import "github.com/gnolang/gno"
+//
+//	|                            __             __
+//	|          ___ ____  ___    / /__ ____  ___/ /
+//	|         / _ `/ _ \/ _ \_ / / _ `/ _ \/ _  /
+//	|         \_, /_//_/\___(_)_/\_,_/_//_/\_,_/
+//	|        /___/
+package readme