chore: add install, usage in README

README.md

@@ -1,12 +1,38 @@
 # gofimports
 
-goimports with my opinionated preferences.
+Group Go imports with my opinionated preferences.
+
+First is standard.
+Then third party, then company if exist.
+The last is local.
+
+Also main selling point of this is group imports not sort imports.
+So please run `gofumpt` or `gofmt` after this.
+
+## Install
+
+With Go version `>= 1.16`:
+
+```sh
+go install github.com/haunt98/gofimports/cmd/gofimports@latest
+```
+
+## Usage
+
+```sh
+# Format ./internal
+# with print impacted file (-l),
+# write to file (-w),
+# print diff (-d)
+# company is github.com/make-go-great
+gofimports -l -company github.com/make-go-great -w -d ./internal
+```
 
 ## Roadmap
 
 - [ ] Diff with color
 - [ ] Add profiling
-- [ ] Use profiling to improve performance
+- [ ] Improve performance
 
 ## Thanks