broken link in docs & readme

[jairav]

Docs Location:

• Verily Custom Apps Docs
• In the section "Create your own app with dev containers" link to Workbench template
• 404

Readme:

• Reference example app points to https://github.com/verily-src/workbench-app-devcontainer/tree/main/src/example
• Should be https://github.com/verily-src/workbench-app-devcontainers/tree/master/src/example