minor #1494 Bootstrapping an UPGRADE log (weaverryan)

This PR was squashed before being merged into the 2.x branch.

Discussion
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Bootstrapping an UPGRADE log

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Issues        | None
| License       | MIT

As suggested by `@smnandre`, a CHANGELOG. This would be for things that user should actually change from one version to another. symfony/symfony maintains something similar.

Commits
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58de823 Bootstrapping an UPGRADE log

Author: weaverryan

UPGRADE.md

@@ -0,0 +1,5 @@
+# UPGRADE
+
+## FROM 2.14 to 2.15
+
+-   **Live Components**: Change `data-live-id` attributes to `id` #1484.