add readme

README.md

@@ -0,0 +1,28 @@
+# go-pgp-tool
+
+## Usage
+build code
+```bash
+$ go build -o go-pgp-tool main.go
+```
+show usage
+```bash
+$ ./go-pgp-tool -h
+```
+
+### options
+```
+  Usage options:
+    -h show usage
+    -d decrypt mode
+    -e encrypt mode
+    -y force override output file
+    -p password
+      private key password with decrypt usage
+    -i file path
+      source file path
+    -o file path
+      output file path
+    -k file path
+      key file path
+```