doc(CHANGELOG.md): add changelog for beta2

Author: Aaron Schlesinger

CHANGELOG.md

@@ -0,0 +1,14 @@
+### v2.0.0-beta1 -> v2.0.0-beta2
+
+#### Features
+
+ - [`d555f3a`](https://github.com/deis/workflow/commit/d555f3a81cae17a7537766686c428a4358740e7a) storage: change docs to use deis-object-storage-secret for configuring database
+ - [`abd3279`](https://github.com/deis/workflow/commit/abd32796e908f8b71629a373a8b5a05e198cf156) managing-deis: lazy pass at upgrading workflow
+ - [`7a32ce8`](https://github.com/deis/workflow/commit/7a32ce826713980e13476c7b5e840635e350d09b) healthchecks: improve healthcheck documentation, add new options and include defaults
+ - [`c71b596`](https://github.com/deis/workflow/commit/c71b596ab44bb26c7e1a84f13fb3bcb3050243c0) mkdocs: enable toc extension
+ - [`614a487`](https://github.com/deis/workflow/commit/614a487936b41aea2f288bf656b9f5fa9eee7009) docker: add .dockerignore
+ - [`5652eef`](https://github.com/deis/workflow/commit/5652eeff2643387f204eff93fadc34982a97b165) storage: change docs to use deis-object-storage-secret for configuring the storage
+
+#### Fixes
+
+ - [`9cd65e6`](https://github.com/deis/workflow/commit/9cd65e65972a98c515b28218f3e2d454206fb751) CONTRIBUTING: fix broken links