Flesh out README.md

Author: moolmanruan

README.md

@@ -1,3 +1,46 @@
-### Installation
+# Danger in Go
 
-`go install github.com/moolmanruan/danger-go/cmd/danger-go@latest`
+This is a Go version of the popular Danger tool.
+
+## Installation of command line tool
+
+```shell
+go install github.com/moolmanruan/danger-go/cmd/danger-go@latest
+yarn global add danger
+```
+
+Requires [Danger JS](https://danger.systems/js) to run properly.
+
+## Integrate into project
+
+1. Create a new directory to house the *dangerfile.go* file. This repo uses `build/ci`.
+2. Add a `dangerfile.go` to the directory with the following contents:
+```go
+package main
+
+import (
+	"fmt"
+
+	"github.com/moolmanruan/danger-go"
+	"github.com/moolmanruan/danger-go/danger-js"
+)
+
+func Run(d *danger.T, pr dangerJs.DSL) {
+	d.Message("danger-go is running!", "", 0)
+}
+```
+3. Run the following in the directory:
+```shell
+go mod init dangerfile
+go get github.com/moolmanruan/danger-go
+go mod tidy
+```
+
+## Running danger-go locally
+
+The `danger-go` command line tool supports `local`, `pr`, and `ci` commands. `danger-go` wraps the corresponding `danger` (js) commands, so to get information about flags, run `danger <command> --help`.
+
+## CI integration
+
+### GitHub Actions
+See `.github/workflows/main.yml` as a reference.