[Documentation]: Some cookbook examples are out-of-date.

[grootpiano]

Describe the issue
Hi, I found some cookbook examples are out-of-date.

After we changed line pkg/api/member.go:76 from buff, err := yaml.Marshal(resp) to buff, err := codectool.MarshalJSON(resp), some grep commands in examples are not worked.

e.g. commands in Getting Started and Easegress cluster cookbook:

$ egctl member list | grep "cluster-role"   # should grep "ClusterRole"
$ egctl member list | grep "api-addr"
$ egctl member list | grep "name"

egctl --server $HOST1:2381 member list | grep " name"

Version
Latest master branch version 73d7dd32.

Additional context
I'm sure that everyone can fix this little tiny issue by themselves. But I also want to make our docs better, at least the
Getting Started part.

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Thanks for contributing 🎉!