Add release notes

RELEASE.md

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+# Cutting a new release of `Wac`
+
+To cut a new release, you will need to do the following:
+
+1. Confirm that [CI is green](https://github.com/bytecodealliance/wac/actions) for the commit selected to be tagged and released.
+
+2. Change the workspace version number in [Cargo.toml](./Cargo.toml).
+
+3. Create a pull request with these changes and merge once approved.
+
+4. Checkout the commit with the version bump from above.
+
+5. Create and push a new tag with a `v` and then the version number.
+
+    As an example, via the `git` CLI:
+
+    ```
+    # Create a GPG-signed and annotated tag
+    git tag -s -m "Wac v0.8.0" v0.8.0
+
+    # Push the tag to the remote corresponding to bytecodealliance/wac (here 'origin')
+    git push origin v0.8.0
+    ```
+
+6. Pushing the tag upstream will trigger the release actions which creates a release and publishes the crates in this workspace to `crates.io`