e2e Test documentation for FE onboarding (#1681)

* Add e2e documentation to faciltiate FE devs onboarding

Co-authored-by: Michael Li <michael.li@hashicorp.com>
Co-authored-by: lisbet-alvarez <107949262+lisbet-alvarez@users.noreply.github.com>

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Co-authored-by: Michael Li <michael.li@hashicorp.com>
Co-authored-by: lisbet-alvarez <107949262+lisbet-alvarez@users.noreply.github.com>

ui/admin/package.json

@@ -10,7 +10,7 @@
     "test": "tests"
   },
   "scripts": {
-    "doc:toc": "doctoc README.md",
+    "doc:toc": "doctoc README.md tests/e2e/README.md",
     "build:development": "ember build",
     "build": "ember build --environment=production",
     "build:oss": "EDITION=oss ember build --environment=production",