docs: Update multichain-testing README.md (#9917)

closes: #XXXX
refs: #XXXX

## Description
The `make clean setup` command specified in `multichain-testing` README always fails if you're setting it up for the first time due to "clean" trying to do cleanup using binaries that do not exist. 

Secondly, the `make override-chain-registry` also fails due to the absence of dependencies (`tsx` in particular). 

This PR attempts to update the `Initial Setup` section to fix these cases. 

### Security Considerations


### Scaling Considerations


### Documentation Considerations


### Testing Considerations


### Upgrade Considerations

multichain-testing/Makefile

@@ -61,7 +61,7 @@ setup-kind:
 
 .PHONY: clean-kind
 clean-kind:
-	kind delete cluster --name $(KIND_CLUSTER)
+	-kind delete cluster --name $(KIND_CLUSTER)
 
 ###############################################################################
 ###                          Agoric Setup                                   ###

multichain-testing/README.md

@@ -16,7 +16,13 @@ The `agoric` software revision includes the vats necessary for building and test
 
 ## Initial Setup
 
-First, ensure you have Kubernetes available. See https://docs.cosmology.zone/starship/get-started/step-2.
+Install the relevant dependencies:
+
+```sh
+yarn install
+```
+
+Ensure you have Kubernetes available. See https://docs.cosmology.zone/starship/get-started/step-2.
 
 The following will install `kubectl`, `kind`, `helm`, and `yq` as needed.