Merge pull request #2326 from nspcc-dev/doc-go-mod-compiler-requirement

docs: mention go modules, fix #2274

docs/compiler.md

@@ -54,6 +54,13 @@ this requires you to set proper `GOROOT` environment variable, like
 export GOROOT=/usr/lib64/go/1.15
 ```
 
+You'll also need to initialize go modules for your contract like this (in the
+directory containing contract package):
+```
+$ go mod init
+$ go mod tidy
+```
+
 ### Compiling
 
 ```