Update README

Author: chaspy

README.md

@@ -15,3 +15,59 @@ $ cp .envrc.sample .envrc
 |----|-------|-----------|
 |AWS_API_INTERVAL|300|Duration time to call AWS API (in seconds)|
 |IMAGE_TAGS|""|Image Tags of the scan target, separated by comma|
+
+## How to run
+
+### Local
+
+```
+$ go run main.go
+```
+
+### Binary
+
+Get the binary file from [Releases](https://github.com/chaspy/aws-ecr-image-scan-findings-prometheus-exporter/releases) and run it.
+
+### Docker
+
+```
+$ docker run chaspy/aws-ecr-image-scan-findings-prometheus-exporter:v0.1.0
+```
+
+## Metrics
+
+```
+$ curl -s localhost:8080/metrics | grep aws_custom_ecr_image_scan_findings
+# HELP aws_custom_ecr_image_scan_findings ECR Image Scan Findings
+# TYPE aws_custom_ecr_image_scan_findings gauge
+aws_custom_ecr_image_scan_findings{CVSS2_SCORE="9.3",CVSS2_VECTOR="AV:N/AC:M/Au:N/C:C/I:C/A:C",image_tag="production",name="CVE-2019-2201",package_name="1:1.5.2-2",package_version="1:1.5.2-2",repo_name="rails",severity="LOW"} 1
+aws_custom_ecr_image_scan_findings{CVSS2_SCORE="9.3",CVSS2_VECTOR="AV:N/AC:M/Au:N/C:C/I:C/A:C",image_tag="production",name="CVE-2019-2201",package_name="1:1.5.2-2",package_version="1:1.5.2-2",repo_name="nginx",severity="LOW"} 1
+aws_custom_ecr_image_scan_findings{CVSS2_SCORE="9.3",CVSS2_VECTOR="AV:N/AC:M/Au:N/C:C/I:C/A:C",image_tag="develop",name="CVE-2020-8174",package_name="10.23.0-1nodesource1",package_version="10.23.0-1nodesource1",repo_name="api",severity="CRITICAL"} 1
+aws_custom_ecr_image_scan_findings{CVSS2_SCORE="9.3",CVSS2_VECTOR="AV:N/AC:M/Au:N/C:C/I:C/A:C",image_tag="develop",name="CVE-2020-8174",package_name="4.8.2~dfsg-1",package_version="4.8.2~dfsg-1",repo_name="example",severity="CRITICAL"} 1
+```
+
+## IAM Role
+
+The following policy must be attached to the AWS role to be executed.
+
+```json
+{
+    "Version": "2012-10-17",
+    "Statement": [
+        {
+            "Sid": "VisualEditor0",
+            "Effect": "Allow",
+            "Action": [
+                "ecr:DescribeRepositories",
+                "ecr:DescribeImageScanFindings",
+            ],
+            "Resource": "*"
+        }
+    ]
+}
+```
+
+## Datadog Autodiscovery
+
+If you use Datadog, you can use [Kubernetes Integration Autodiscovery](https://docs.datadoghq.com/agent/kubernetes/integrations/?tab=kubernetes) feature.
+