doc: add build instruction

.gitignore

@@ -1 +1,2 @@
 .DS_Dtore
+dnskip

README.md

@@ -2,6 +2,13 @@
 A simple Golang DoT proxy using TRS.
 
 ## Usage
+
+### Run
 ```bash
 go run -ldflags "-checklinkname=0" main.go
 ```
+
+### Build
+```bash
+go build -ldflags "-s -w -checklinkname=0" -trimpath -o dnskip main.go
+```