Add Subxt explorer (#6352)

Allows for entering custom RPC endpoint and generates docs

docs/general/metadata.md

@@ -15,4 +15,11 @@ The dropdown below allows you to update the chain selection to visualize. You ca
 sub-categories using the provided search field. The information is categorized by the chains
 `Pallets`, `RPC` and `Runtime` information.
 
+:::info Subxt Explorer
+
+You can enter custom RPC endpoints for Polkadot SDK based chains and explore their metadata using 
+[Parity Tech Subxt Explorer](https://paritytech.github.io/subxt-explorer/#/).
+
+:::
+
 <Metadata version="V14"/>