merge docs

Author: skudasov

book/src/framework/fork_storage.md

@@ -0,0 +1,26 @@
+# Fork Testing (Mutating Storage)
+
+We provide API to use `anvil_setStorageAt` more easily so in case you can't edit EVM smart contracts code you can still mutate your contract values.
+
+You need to build your contract layout first
+```
+forge build || forge inspect Counter storageLayout --json > layout.json
+```
+
+And then you can use `AnvilSetStorageAt` to override contract's storage data
+```
+		r := rpc.New(rpcURL, nil)
+		err = r.AnvilSetStorageAt([]interface{}{contractAddr, slot, data})
+```
+See [examples](https://github.com/smartcontractkit/chainlink-testing-framework/blob/main/framework/evm_storage/layout_api_test.go) of how you can use API to encode/mutate different values.
+
+Keep in mind that values <32 bytes are packed together, see `encodeCustomStructFunc` example and `offset` example to understnad how to change them properly.
+
+```
+cd framework/evm_storage
+./setup.sh
+go test -v -run TestLayoutAPI
+./teardown.sh
+```
+
+Read more about Solidity storage layout [here](https://docs.soliditylang.org/en/latest/internals/layout_in_storage.html#)