Allocator client tutorial: add steps for MacOS

[aLekSer]

Minor fix of argument and summarize all environment vars together to be
used by shell script.
Tested that all steps could be performed on MacOS.

What type of PR is this?

/kind documentation

What this PR does / Why we need it:
Fixes Tutorial for MacOS.

Which issue(s) this PR fixes:

Special notes for your reviewer:
Results of running the bash script:

 ./test.sh
response: state:Allocated gameServerName:"simple-udp-phptn-6kd8m" ports:<name:"default" port:7947 > address:"35.197.45.57" nodeName:"gke-test-cluster-default-ac24bb9b-hhsl"

[agones-bot]

Build Succeeded 👏

Build Id: 94350d96-a8c3-4245-9ec2-4921d434d29d

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.6.0-650f80b
• image: gcr.io/agones-images/agones-sdk:1.6.0-650f80b
• image: gcr.io/agones-images/agones-ping:1.6.0-650f80b
• Linux C++ SDK (build): agonessdk-1.6.0-650f80b-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-650f80b.zip

A preview of the website (the last 30 builds are retained):

• https://650f80b-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1484/head:pr_1484 && git checkout pr_1484
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-650f80b

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aLekSer, pooneh-m

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