chore(docs): fix broken link in tm2/pkg/amino/README.md (#2322)

This is a broken link:


https://github.com/gnolang/gno/blob/3f5a6ad90600fef16a04675d79e4ef8f0e19bf4d/tm2/pkg/amino/README.md?plain=1#L46-L50

PR replaces it with the updated link.

<details><summary>Details</summary>
<p>
File was move there:

https://github.com/tendermint/tendermint/blob/main/spec/blockchain/encoding.md

which says it's been moved there:

https://github.com/tendermint/tendermint/blob/main/spec/core/encoding.md

</p>
</details> 

---
For the future, since we have a version in the monorepo and
gnolang/tendermint2, where is the best place to post PR?

Because gnolang/tendermint2 of course has the same issue
(https://github.com/gnolang/tendermint2/blob/master/pkgs/amino/README.md)

Co-authored-by: grepsuzette <[email protected]>

tm2/pkg/amino/README.md

@@ -45,8 +45,7 @@ This is experimental and subject to change.
 
 ## Amino in the Wild
 
-* Amino:binary spec in [Tendermint](
-https://github.com/tendermint/tendermint/blob/master/docs/spec/blockchain/encoding.md)
+* Amino:binary spec in [Tendermint](https://github.com/tendermint/tendermint/blob/main/spec/core/encoding.md)
 
 
 # Amino Spec