chore: update S3 upload path and document AWS config

.envrc.example

@@ -2,3 +2,5 @@ export DATABASE_USERNAME=postgres
 export DATABASE_PASSWORD=postgres
 export ARROW_DOMAIN=https://arrow.mbta.com
 export ARROW_API_KEY=
+export AWS_ACCESS_KEY_ID=
+export AWS_SECRET_ACCESS_KEY=

README.md

@@ -23,6 +23,7 @@
 - `direnv allow`
 - `cp .envrc.example .envrc`
 - Update `.envrc` with your local Postgres username and password
+- Update `.envrc` with your AWS credentials or ensure they are available in your shell
 - `mix ecto.setup`
 - `brew install chromedriver`
 - Add your Arrow API key from https://arrow.mbta.com/mytoken to `.envrc`

config/dev.exs

@@ -77,7 +77,7 @@ config :arrow, dev_routes: true
 # Set prefix env for s3 uploads
 config :arrow,
   shape_storage_enabled?: true,
-  shape_storage_prefix_env: "local/"
+  shape_storage_prefix_env: "dev/local/"
 
 # Do not include metadata nor timestamps in development logs
 config :logger, :console, format: "[$level] $message\n"