Add missing "/reserve" endpoint description

[aLekSer]

Add curl example for making /reserve request.

[agones-bot]

Build Succeeded 👏

Build Id: e3501813-8f60-4797-89a5-577fd870b9f6

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

• image: gcr.io/agones-images/agones-controller:1.1.0-fe1eff1
• image: gcr.io/agones-images/agones-sdk:1.1.0-fe1eff1
• image: gcr.io/agones-images/agones-ping:1.1.0-fe1eff1
• Linux C++ SDK (build): agonessdk-1.1.0-fe1eff1-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.1.0-fe1eff1.zip

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

• https://fe1eff1-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1083/head:pr_1083 && git checkout pr_1083
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.1.0-fe1eff1

[agones-bot]

Build Succeeded 👏

Build Id: c2f2ffee-3971-4793-abc4-9264181d21bb

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

• image: gcr.io/agones-images/agones-controller:1.1.0-2e6059b
• image: gcr.io/agones-images/agones-sdk:1.1.0-2e6059b
• image: gcr.io/agones-images/agones-ping:1.1.0-2e6059b
• Linux C++ SDK (build): agonessdk-1.1.0-2e6059b-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.1.0-2e6059b.zip

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

• https://2e6059b-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1083/head:pr_1083 && git checkout pr_1083
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.1.0-2e6059b

[markmandel]

Excellent catch.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: aLekSer, markmandel
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