docs: add instructions for authenticating for system tests (#212)

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Synth log will be available here:
https://source.cloud.google.com/results/invocations/959b7829-922a-41dc-a5a7-1178c3a8f0e7/targets

- [ ] To automatically regenerate this PR, check this box.

Source-Link: googleapis/synthtool@363fe30

Author: yoshi-automation

CONTRIBUTING.md

@@ -37,6 +37,13 @@ accept your pull requests.
 1.  Title your pull request following [Conventional Commits](https://www.conventionalcommits.org/) styling.
 1.  Submit a pull request.
 
+### Before you begin
+
+1.  [Select or create a Cloud Platform project][projects]. 
+1.  [Set up authentication with a service account][auth] so you can access the
+    API from your local workstation.
+
+
 ## Running the tests
 
 1.  [Prepare your environment for Node.js setup][setup].
@@ -51,15 +58,17 @@ accept your pull requests.
         npm test
 
         # Run sample integration tests.
-        gcloud auth application-default login
         npm run samples-test
 
         # Run all system tests.
-        gcloud auth application-default login
         npm run system-test
 
 1.  Lint (and maybe fix) any changes:
 
         npm run fix
 
 [setup]: https://cloud.google.com/nodejs/docs/setup
+[projects]: https://console.cloud.google.com/project
+[billing]: https://support.google.com/cloud/answer/6293499#enable-billing
+
+[auth]: https://cloud.google.com/docs/authentication/getting-started

synth.metadata

@@ -4,66 +4,15 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/teeny-request.git",
-        "sha": "84812cdc9445e5cc25e86f9ac9d4c0486a9f2a24"
+        "sha": "072b25ec847e9a5aa597836ad35ab85450b757f7"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "ba9918cd22874245b55734f57470c719b577e591"
+        "sha": "363fe305e9ce34a6cd53951c6ee5f997094b54ee"
       }
     }
-  ],
-  "generatedFiles": [
-    ".eslintignore",
-    ".eslintrc.json",
-    ".gitattributes",
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-    ".github/ISSUE_TEMPLATE/feature_request.md",
-    ".github/ISSUE_TEMPLATE/support_request.md",
-    ".github/PULL_REQUEST_TEMPLATE.md",
-    ".github/release-please.yml",
-    ".github/workflows/ci.yaml",
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 }