-pkg-doc PATH=TEMPLATE

Use the -pkg-doc flag to teach doc2go where to find documentation
for dependencies.
PATH is an import path, and TEMPLATE is a text/template.
Packages with the import path PATH, and any package under it
will use TEMPLATE to generate links to themselves.

TEMPLATE is executed with the following context:

	struct {
		// Import path of the target package.
		ImportPath string
	}

For example:

	-pkg-doc example.com=https://go.example.com/{{.ImportPath}}

This will use go.example.com for all packages under example.com.

	example.com/foo     => https://go.example.com/example.com/foo
	example.com/bar/baz => https://go.example.com/example.com/bar/baz

Pass this flag multiple times to set different templates
for different package scopes.
If two PATHs overlap, the more specific of the two will be used.
For example, given:

	-pkg-doc golang.org/x=https://godocs.io/{{.ImportPath}}
	-pkg-doc golang.org/x/tools=https://pkg.go.dev/{{.ImportPath}}

All packages under golang.org/x/ will use https://godocs.io,
except golang.org/x/tools which will use https://pkg.go.dev.
