Fix instructions for running multiple PXEs

[jzaki]

Docs link here, has not worked as reported by community for some time.

• Consider hiding in docs to avoid negative dev experiences
• Find way to make multiple PXEs work again (if still intended+possible)
• Document how to debug with multiple PXEs

[Thunkar]

To make it work with the new CLI refactor, the commands in the docs should be:

cd ~/.aztec && docker-compose -f ./docker-compose.sandbox.yml up

and

aztec start --port 8081 --pxe nodeUrl=http://host.docker.internal:8080/

This would mean there's a PXE listening on http://localhost:8080 and another one on http://localhost:8081. I still think some context/examples are missing and would be good to actually make this page useful

[grasshopper47]

docker run                    \
  --rm                        \
  --workdir "$PWD"            \
  -e AZTEC_PORT=$1            \
  -e AZTEC_NODE_URL="$2"      \
  -v $HOME:$HOME              \
  -v cache:/cache             \
  -p $1:$1                    \
  aztecprotocol/aztec:latest  \
  start --pxe

this docker command works on all versions