update changelog for 0.2.1

Summary: Updated CHANGELOG.md for 0.2.1 release.

Reviewed By: tierex

Differential Revision: D24113918

fbshipit-source-id: 31424659181bf0badd38e1698b1e371001a52fb3

Author: Kiuk Chung

CHANGELOG.md

@@ -1,10 +1,36 @@
 # CHANGELOG
 
-## 0.1.0rc1 (December 06, 2019)
+## 0.2.1 (October 05, 2020)
 
 ### PyTorch Elastic
 
-* First release torchelastic v0.1.0rc1 (experimental)
+> **_NOTE:_** As of torch-1.7 and torchelastic-0.2.1 torchelastic will be bundled into the main [pytorch docker](https://hub.docker.com/r/pytorch/pytorch)
+   image. [torchelastic/examples](https://hub.docker.com/r/torchelastic/examples) will be available post torch-1.7 release since
+   its base image will now be **pytorch/pytorch**
+
+* Torchelastic agent:
+  * `run_id` available to workers as `TORCHELASTIC_RUN_ID` environment variable
+  * Allow `max_restarts=0`
+  * Worker exit barrier added to torchelastic agent to protect against variances in worker finish times
+  * Improvements to error handling and propagation from torchelastic agent
+  * Enable fault handlers on worker processes to get torch C++ stack traces
+
+* `torchelastic.distributed.launch` CLI:
+   * New option `--role` to allow users to set worker role name
+   * CLI options can now be set via environment variables (e.g. `PET_NNODES="1:2"`)
+   
+* Project:
+  * Upgraded to Python 3.8
+  * Tests moved to `test` directory within the respective modules
+  * Use Pyre
+  
+* Deprecated:
+  * [pytorch/elastic](https://hub.docker.com/r/pytorch/elastic) Docker image
+
+* Experimental:
+  * [Training Session Manager (TSM)](http://pytorch.org/elastic/0.2.1/tsm_driver.html)  with localhost scheduler
+  * [torchelastic.multiprocessing](http://pytorch.org/elastic/0.2.1/multiprocessing.html)
+
 
 ## 0.2.0 (April 29, 2020)
 
@@ -13,5 +39,10 @@
 * Separate infrastructure related work from the user script. [DesignDoc]
 * Events API
 
-
 [DesignDoc]: https://github.com/pytorch/elastic/blob/master/design/torchelastic/0.2.0/design_doc.md
+
+## 0.1.0rc1 (December 06, 2019)
+
+### PyTorch Elastic
+
+* First release torchelastic v0.1.0rc1 (experimental)