[aws-for-fluent-bit] Add serviceAccount.annotations parameter to README

[espizo]

Issue

#395

Description of changes

Updated README.md with the following changes:

• Removed duplicate serviceAccount.create parameter from the Configuration section
• Added serviceAccount.annotations parameter to the Configuration section to reflect the availability of this, ref. https:/aws/eks-charts/blob/master/stable/aws-for-fluent-bit/templates/serviceaccount.yaml#L9-L12

Checklist

• Added/modified documentation as required (such as the README.md for modified charts)
• Incremented the chart version in Chart.yaml for the modified chart(s)
• Manually tested. Describe what testing was done in the testing section below
• Make sure the title of the PR is a good description that can go into the release notes

Testing

This functionality already exists, so I verified that it works with:

helm upgrade --install aws-for-fluent-bit eks/aws-for-fluent-bit \
    --namespace kube-system \
    --set serviceAccount.annotations."eks\.amazonaws\.com/role-arn"="dummy-role-arn"

And then:

$ kubectl get serviceaccount aws-for-fluent-bit -n kube-system -o yaml | head -n5
apiVersion: v1
kind: ServiceAccount
metadata:
  annotations:
    eks.amazonaws.com/role-arn: dummy-role-arn

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[hossain-rayhan]

LGTM. Thanks.