add options output to readme

dynamo-backup-to-s3/README.md

@@ -6,7 +6,7 @@ This is a minimal image built on Alpine Linux and nodejs to run
 ## Usage
 
 ```
-docker run -d --name dynamo-backup-to-s3 \
+$ docker run -d --name dynamo-backup-to-s3 \
   -e AWS_ACCESS_KEY_ID \
   -e AWS_SECRET_ACCESS_KEY \
   -e AWS_DEFAULT_REGION \
@@ -17,3 +17,25 @@ docker run -d --name dynamo-backup-to-s3 \
 
 It is generally preferable to deploy to an ec2 instance with a
 suitable IAM role rather than passing AWS secrets in the environment.
+
+## Options
+
+```
+$ docker run rlister/dynamo-backup-to-s3:latest -h
+
+  Usage: dynamo-backup-to-s3 [options]
+
+  Options:
+
+    -h, --help                       output usage information
+    -V, --version                    output the version number
+    -b, --bucket <name>              S3 bucket to store backups
+    -s, --stop-on-failure            specify the reporter to use
+    -r, --read-percentage <decimal>  specific the percentage of Dynamo read capacity to use while backing up. default .25 (25%)
+    -x, --excluded-tables <list>     exclude these tables from backup
+    -i, --included-tables <list>     only backup these tables
+    -p, --backup-path <name>         backup path to store table dumps in. default is DynamoDB-backup-YYYY-MM-DD-HH-mm-ss
+    --aws-key                        AWS access key. Will use AWS_ACCESS_KEY_ID env var if --aws-key not set
+    --aws-secret                     AWS secret key. Will use AWS_SECRET_ACCESS_KEY env var if --aws-secret not set
+    --aws-region                     AWS region. Will use AWS_DEFAULT_REGION env var if --aws-region not set
+```