gopls/doc: clarify go work use

Author: angaz

gopls/doc/workspace.md

@@ -34,12 +34,14 @@ your workspace root to the directory containing the `go.work` file.
 
 For example, suppose this repo is checked out into the `$WORK/tools` directory.
 We can work on both `golang.org/x/tools` and `golang.org/x/tools/gopls`
-simultaneously by creating a `go.work` file:
+simultaneously by creating a `go.work` file using `go work init`, followed by
+`go work use MODULE_DIRECTORIES...` to add directories containing `go.mod` files to the
+workspace:
 
-```
+```sh
 cd $WORK
 go work init
-go work use tools tools/gopls
+go work use ./tools/ ./tools/gopls/
 ```
 
 ...followed by opening the `$WORK` directory in our editor.