M0011 package not found

example $ marmot build .
error[M0011]: no required module provides package example.com/lib
 --> ./main.go:3:8
  |
3 | import "example.com/lib" // not in go.mod
  |        ^^^^^^^^^^^^^^^^^
  |
  = help: add the module: `go get example.com/lib`

error: build failed with 1 error
for more about an error, run `marmot explain M0011`

package main

import "example.com/lib" // not in go.mod

func main() {}