Update 'go-cheatsheet.md'

go-cheatsheet.md

@@ -1,5 +1,26 @@
 # go (golang) cheatsheet
 
+## tools and environment
+
+goimports manages your import lines and should be used instead of fmt, golangci-lint will tell you when you're doing silly things, and gotest will do the same thing as `go test` but with color output in terminal.
+
+```
+go get golang.org/x/tools/cmd/goimports
+go get github.com/golangci/golangci-lint/cmd/golangci-lint@v1.31.0
+go get -u github.com/rakyll/gotest
+```
+
+## code style
+
+* obviously, always gofmt
+* run golangci-lint
+
+## types and interfaces
+
+Accept and provide `String() string` method and the associated `fmt.Stringer` interface.
+
+Accept and provide `GoString() string` method so `%#v` (see below) works right.
+
 ## testing
 
 ### use testify