Update readme

README.md

@@ -5,6 +5,9 @@ My site <http://www.jonashietala.se>.
 # Sync
 
 1. Setup an AWS credentials file or add environment variables. [Docs](https://docs.rs/aws-creds/latest/awscreds/struct.Credentials.html).
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+   By default it will use `~/.aws/credentials` if exists.
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 2. `./blog sync` to sync `.output` and `./blog upload-files` to upload files not tracked by git.
 
 # Syntax highlighting