docs: update README

README.md

@@ -1,19 +1,43 @@
 # golang-cross [![Actions Status](https://github.com/gythialy/golang-cross/workflows/Docker%20Image%20CI/badge.svg)](https://github.com/gythialy/golang-cross/actions)
 
-Docker container to do cross compilation (Linux, windows, macOS, ARM, ARM64) of go packages including support for cgo. 
+Docker container to do cross compilation (Linux, windows, macOS, ARM, ARM64) of go packages including support for cgo.
 
-## Docker
+## Docker images
 
-Find it on docker hub https://hub.docker.com/r/goreng/golang-cross or run 
+- Find it on docker hub
+
+  - [golang-cross](https://hub.docker.com/r/goreng/golang-cross)
+    ```
+    docker pull goreng/golang-cross
+    ```
+  - [golang-cross-builder](https://hub.docker.com/r/goreng/golang-cross-builder)
+    ```
+    docker pull goreng/golang-cross-builder
+    ```
+
+- Build your own images
+  - Build base image (optional)
+    ```
+     docker build -f Dockerfile_builder -t goreng/golang-cross-builder:1.15.1 .
+    ```
+    > Please follow the guide to [pack the SDK](https://github.com/tpoechtrager/osxcross#packaging-the-sdk) first
+  - Build golang-cross image
+    ```
+    docker build --build-arg GOLANG_VERSION=1.15.6 --build-arg GOLANG_DIST_SHA=3918e6cc85e7eaaa6f859f1bdbaac772e7a825b0eb423c63d3ae68b21f84b844 --build-arg GORELEASER_VERSION=0.149.0 --build-arg GORELEASER_SHA=a227362d734cda47f7ebed9762e6904edcd115a65084384ecfbad2baebc4c775 -f Dockerfile -t goreng/golang-cross .
+    ```
+    > The default arguments can be overridden with `--build-arg`
+## How to use
+
+- Prepare [GoReleaser](https://goreleaser.com/intro/) configuration
+
+- Generate environment variable `PRIVATE_KEY` from the GPG private key (optional), if enable the [signing](https://goreleaser.com/customization/sign/) feature
 
-- generate evn var from file
-
   ```bash
   export PRIVATE_KEY=$(cat ~/private_key.gpg | base64)
   ```
 
-- run docker container
-  
+- Run docker container to build the binaries
+
   ```bash
   docker run --rm --privileged \
     -e PRIVATE_KEY=${PRIVATE_KEY} \
@@ -22,3 +46,12 @@ Find it on docker hub https://hub.docker.com/r/goreng/golang-cross or run
     -w /go/src/github.com/qlcchain/go-qlc \
     goreng/golang-cross:latest --snapshot --rm-dist
   ```
+
+## Practical Examples
+
+- [.goreleaser.yml](https://github.com/qlcchain/go-qlc/blob/master/.goreleaser.yml)
+- [Makefile](https://github.com/qlcchain/go-qlc/blob/master/Makefile#L50-L67)
+
+## Thanks
+
+[![Jetbrains](assets/jetbrains-variant-3.svg)](https://www.jetbrains.com/?from=golang-cross)