Bump version to 0.2.0 (#1919)

Author: wwwjn

assets/version.txt

@@ -1 +1 @@
-0.1.0
+0.2.0

docs/release.md

@@ -5,6 +5,7 @@ Currently we follow a lightweight release process.
     - if major features are added, increment `y`
     - if minor fixes are added, increment `z`
 - Create a new release at https://github.com/pytorch/torchtitan/releases/new
+  - In the tag section, add a new tag for the release. The tag should use the version number with a `v` prefix (for example, `v0.1.0`). Make sure to select the `main` branch as the target.
   - In the release notes
     - include proper nightly versions for `torch` and `torchao`, which can be found in [latest CI](https://github.com/pytorch/torchtitan/actions/workflows/integration_test_8gpu.yaml) test log "Run script in container" section. E.g.
         - "Successfully installed ... `torch-2.8.0.dev20250605+cu126`"