docs: reorganize application distribution links in table of contents (#18744)

* docs: fix link to supported platforms in TOC

* docs: move code signing under the distribution heading

docs/README.md

@@ -63,10 +63,9 @@ an issue:
   * [Testing on Headless CI Systems (Travis, Jenkins)](tutorial/testing-on-headless-ci.md)
   * [DevTools Extension](tutorial/devtools-extension.md)
   * [Automated Testing with a Custom Driver](tutorial/automated-testing-with-a-custom-driver.md)
-* Packaging
-  * [Code Signing](tutorial/code-signing.md)
 * [Distribution](tutorial/application-distribution.md)
-  * [Support](tutorial/support.md)
+  * [Supported Platforms](tutorial/support.md#supported-platforms)
+  * [Code Signing](tutorial/code-signing.md)
   * [Mac App Store](tutorial/mac-app-store-submission-guide.md)
   * [Windows Store](tutorial/windows-store-guide.md)
   * [Snapcraft](tutorial/snapcraft.md)