Updated test analytics doc for more details on how to read the data (#15494)

## DESCRIBE YOUR PR
Added a new section with details on how to read the trickier data on the
dashboard.

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## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
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---------

Co-authored-by: Shannon Anahata <shannonanahata@gmail.com>
Co-authored-by: Tom Hu <88201630+thomasrockhu-codecov@users.noreply.github.com>

Author: 3 people

docs/product/test-analytics/img/all-branches-dash.png

@@ -90,15 +90,27 @@ Now that you've configured your CI to upload your test results, you can inspect
 
 After your workflow runs, view failed tests in the [failed tests dashboard](https://sentry.io/prevent/tests/?filterBy=failedTests), or in your GitHub pull request comments.
 
-![Test Analytics comment](./img/TA-comment.png)
+![Test Analytics comment =800x](./img/TA-comment.png)
 
-You can see a complete overview of your test analytics in the [test analytics dashboard](https://sentry.io/prevent/tests/). **Note**: The `All Branches`dashboard refreshes every 24 hours.
+### Reading Test Analytics Data
+You can see a complete overview of your test analytics in the [test analytics dashboard](https://sentry.io/prevent/tests/).     
+**Note**: The `All Branches`dashboard refreshes every 24 hours.
+
+![ALl branches dashboard](./img/all-branches-dash.png)
+
+- `Failed Tests`: Shows all failed tests across all branches. Because of this, the _total run time_ may be higher than the filtered time range selected.
+- `Flaky Tests`: These are tests that go from fail to pass or pass to fail compared to the default branch. This analysis will only run when: 
+  - The commit is merged to the default branch
+  - Flake detection is enabled on your yaml (default is true)
+  - Either: The repo is public (regardless of plan type); Or: The repo is private, and is above free or team plan types
+- `Cumulative Failures`: Shows the number of individual test failures, only on the default branch.
 
 ##  Permissions and Repository Tokens
 When configuring Test Analytics, you'll be asked to choose your upload permissions. For GitHub Actions, you can use [OpenID Connect](https://docs.github.com/en/actions/security-for-github-actions/security-hardening-your-deployments/about-security-hardening-with-openid-connect), or generate a repository token. Using the CLI, generate a repository token.
 
 You can find a list of repository tokens on the Sentry Prevent [tokens page](https://sentry.io/prevent/tokens/).
 
+
 ## Read Next
 
 <PageGrid />