add readme

README.MD

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+# Golang Delete AWS ECR Image Tool
+
+## Compile Code
+``` bash
+$ go get -v -u ./...
+$ go build -o go-ecr-delete-image .
+```
+
+## Usage
+```bash
+$ ./go-ecr-delete-image -h 
+Usage of ./go-ecr-delete-image:
+  -e value
+    	exlude delete tag
+  -keep int
+    	keep number images (default 5)
+  -list-repo
+    	list all repository
+  -profile string
+    	aws config profile
+  -repo string
+    	repository name
+```
+
+## Example 1
+```bash
+# use env pass access_key and secret_key
+$ AWS_ACCESS_KEY=key AWS_SECRET_KEY=key ./go-ecr-delete-image -e exclude1 -e exclude2 -repo repoName -keep 5
+```
+
+## Example 2
+```bash
+# use aws configure
+$ ./go-ecr-delete-image -profile default -e exclude1 -e exclude2 -repo repoName -keep 5
+```