Document that Install Cloud SDK only works on Windows. (#57)

Add comments indicating install-cloud-sdk will only work on a windows build agent.

DETAILS.md

@@ -3,10 +3,8 @@
 This extension provides a service endpoint and build tasks to make deploying to
 Google Cloud Platform a breeze.
 
-[TODO(przybjw)]: # (Validate on site documentation link)
-
-Quickstart and How-To documentation can be found at
-https://cloud.google.com/tools/cloud-tools-tfs/docs/community
+[TODO(przybjw) - Uncomment once live]: # (Quickstart and How-To documentation can be found at)
+[TODO(przybjw) - Uncomment once live]: # (https://cloud.google.com/tools/cloud-tools-tfs/docs/community)
 
 
 ## Installation
@@ -42,8 +40,10 @@ The extension installs the following tasks:
   - **[Get Google Compute VM password][set-login-password]**: Gets the IP address
   and user password for a [Google Compute Engine][ComputeEngine] virtual machine
   running windows.
-  - **[Install Google Cloud SDK][install-cloud-sdk]**: Finds or installs the
+  - **[Install Google Cloud SDK][install-cloud-sdk]**: Windows only. Finds or installs the
   [Google Cloud SDK][CloudSdk].
+  - **[Google Cloud SDK Tool Installer][cloud-sdk-tool]**: Installs the [Google Cloud SDK][CloudSdk] as a cached
+  [VSTS Tool][vsts-tool].
 
 [CloudSdk]: https://cloud.google.com/sdk
 [CloudSdkInstall]: https://cloud.google.com/sdk/downloads
@@ -57,3 +57,5 @@ The extension installs the following tasks:
 [container-build]: https://github.com/GoogleCloudPlatform/google-cloud-tfs/blob/master/container-build-task/README.md
 [set-login-password]: https://github.com/GoogleCloudPlatform/google-cloud-tfs/blob/master/set-login-build-task/README.md
 [install-cloud-sdk]: https://github.com/GoogleCloudPlatform/google-cloud-tfs/blob/master/install-cloud-sdk-build-task/README.md
+[cloud-sdk-tool]: https://github.com/GoogleCloudPlatform/google-cloud-tfs/blob/master/cloud-sdk-tool-build-task/README.md
+[vsts-tool]: https://docs.microsoft.com/en-us/vsts/build-release/concepts/process/tasks#tool-installers

install-cloud-sdk-build-task/README.md

@@ -10,6 +10,8 @@ and allows caching of Goolge Cloud SDK versions, but requires the  [VSTS Tool In
 
 ## Usage
 
+This task only works on Windows build agents.
+
 If the Google Cloud SDK is already installed for all users on the build agent,
 this task is unnecessary. If, however, the Google Cloud SDK is installed for
 the build agent user only, or not installed at all, you can use this task to find

install-cloud-sdk-build-task/task.json

@@ -5,21 +5,19 @@
   "friendlyName": "Install Google Cloud SDK",
   "author": "Google Cloud Tools",
   "description": "Installs and configures the Google Cloud SDK.",
-  "helpMarkDown": "The [Google Cloud SDK](https://cloud.google.com/sdk) is required for all Google Cloud Tools for TFS Build tasks.",
+  "helpMarkDown": "The [Google Cloud SDK](https://cloud.google.com/sdk) is required for all Google Cloud Tools for TFS Build tasks. This task will install it on a Windows build agent.",
   "version": {
     "Major": 0,
     "Minor": 0,
     "Patch": 4
   },
   "category": "Utility",
-  "visibility": [ "Build", "Release" ],
   "demands": [],
   "groups": [
     {
       "name": "advanced",
       "displayName": "Advanced",
-      "isExpanded": false,
-      "tags": []
+      "isExpanded": false
     }
   ],
   "inputs": [