PR 239 update: Adding more logging for the initial generate setup (#246)

This is just a tweak to #239 to update the snapshots.
I have:
- [X] Written a clear PR title and description (above)
- [X] Signed the [Khan Academy CLA](https://www.khanacademy.org/r/cla)
- [X] Added tests covering my changes, if applicable
- [X] Included a link to the issue fixed, if applicable
- [X] Included documentation, for new features
- [ ] Added an entry to the changelog

Signed-off-by: Steve Coffman <steve@khanacademy.org>
Co-authored-by: Sam Wallace <29391916+thecasual@users.noreply.github.com>

generate/config.go

@@ -102,12 +102,16 @@ func (c *Config) ValidateAndFillDefaults(baseDir string) error {
 	if c.Package == "" {
 		abs, err := filepath.Abs(c.Generated)
 		if err != nil {
-			return errorf(nil, "unable to guess package-name: %v", err)
+			return errorf(nil, "unable to guess package-name: %v is not a valid identifier"+
+				"\nSet package name in genqlient.yaml"+
+				"\nExample: https://github.com/Khan/genqlient/blob/main/example/genqlient.yaml#L6", err)
 		}
 
 		base := filepath.Base(filepath.Dir(abs))
 		if !token.IsIdentifier(base) {
-			return errorf(nil, "unable to guess package-name: %v is not a valid identifier", base)
+			return errorf(nil, "unable to guess package-name: %v is not a valid identifier"+
+				"\nSet package name in genqlient.yaml"+
+				"\nExample: https://github.com/Khan/genqlient/blob/main/example/genqlient.yaml#L6", base)
 		}
 
 		c.Package = base

generate/convert.go

@@ -524,7 +524,8 @@ func (g *generator) convertDefinition(
 
 		// (If you had an entry in bindings, we would have returned it above.)
 		return nil, errorf(
-			pos, `unknown scalar %v: please add it to "bindings" in genqlient.yaml`, def.Name)
+			pos, "unknown scalar %v: please add it to \"bindings\" in genqlient.yaml"+
+				"\nExample: https://github.com/Khan/genqlient/blob/main/example/genqlient.yaml#L12", def.Name)
 	default:
 		return nil, errorf(pos, "unexpected kind: %v", def.Kind)
 	}

generate/testdata/snapshots/TestGenerateErrors-UnknownScalar-go

@@ -1 +1,2 @@
 testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to "bindings" in genqlient.yaml
+Example: https://github.com/Khan/genqlient/blob/main/example/genqlient.yaml#L12

generate/testdata/snapshots/TestGenerateErrors-UnknownScalar-graphql

@@ -1 +1,2 @@
 testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to "bindings" in genqlient.yaml
+Example: https://github.com/Khan/genqlient/blob/main/example/genqlient.yaml#L12