Add Go workspace related commands

src/golang.md

@@ -34,4 +34,16 @@ go list -f '{{.Target}}'
 ```powershell
 # Update go.mod to point a module to a local directory.
 go mod edit -replace example.com/greetings=../greetings
+
+# Get an external module and add to go.mod require.
+go get golang.org/x/example
+```
+
+## Workspaces
+```powershell
+# Initialize a workspace with an existing module.
+go work init ./hello
+
+# Add a child module directory to the workspace.
+go work use ./example
 ```