doc: mention refreshInterval in the doc

Author: aboutlo

README.md

@@ -124,6 +124,7 @@ return (
 
 You can use `EthSWRConfig` to have a global fetcher capable of retrieving basic Ethereum information (e.g. block, getBalance)
 or directly interact with a smart contract mapped to its ABI.
+To keep the state fresh you can pass `refreshInterval: 30000` to the `value` object so that behind the scene Ether-SWR will refresh every 30 seconds the data of all the keys mounted in the tree components.
 
 ```js
 import React from 'react'
@@ -201,7 +202,7 @@ export const Wallet = () => {
       )}
       {active && chainId && (
         <EthSWRConfig
-          value={{ provider: library, ABIs: new Map(ABIs) }}
+          value={{ provider: library, ABIs: new Map(ABIs), refreshInterval: 30000 }}
         >
           <EthBalance />
           <TokenList chainId={chainId} />

examples/helloworld/src/App.tsx

@@ -172,7 +172,9 @@ export const TokenList = ({ chainId }: { chainId: number }) => {
   const { account } = useWeb3React<Web3Provider>()
   const tokens = TOKENS_BY_NETWORK[chainId]
   // Multiple calls example
-  const { data: balances } = useEtherSWR<BigNumber[]>(tokens.map(t => [t.address, 'balanceOf', account!]))
+  const { data: balances } = useEtherSWR<BigNumber[]>(
+    tokens.map(t => [t.address, 'balanceOf', account!])
+  )
   return (
     <>
       {balances &&
@@ -207,7 +209,11 @@ export const Wallet = () => {
       )}
       {active && chainId && (
         <EthSWRConfig
-          value={{ provider: library, ABIs: new Map(ABIs(chainId)) }}
+          value={{
+            provider: library,
+            ABIs: new Map(ABIs(chainId)),
+            refreshInterval: 30000
+          }}
         >
           <EthBalance />
           <TokenList chainId={chainId} />