document the removal of empty lines surrounding field lists

Our documentation of the rule was actually incorrect.
We always applied it to all field lists, not interfaces.
And we didn't take comments into account yet,
which is what the recent change improved upon.

While here, remove unintentional whitespace from the added tests.

Author: mvdan

README.md

@@ -385,7 +385,7 @@ var _ = map[string]string{
 
 </details>
 
-Interfaces should not have leading or trailing empty lines
+Field lists should not have leading or trailing empty lines
 
 <details><summary><i>example</i></summary>
 
@@ -396,6 +396,12 @@ type Person interface {
 
 	Age() int
 
+}
+
+type ZeroFields struct {
+
+	// No fields are needed here.
+
 }
 ```
 
@@ -405,6 +411,10 @@ type Person interface {
 
 	Age() int
 }
+
+type ZeroFields struct {
+	// No fields are needed here.
+}
 ```
 
 </details>

testdata/scripts/block-empty.txt

@@ -25,16 +25,16 @@ func f() {
 
 
 		// lone comment
-		
-		
+
+
 	}
 
 	type I interface {
 
 
 		// lone comment
-		
-		
+
+
 	}
 
 
@@ -43,19 +43,16 @@ func f() {
 type SOut struct {
 
 	// lone comment
-	
+
 }
 
 type IOut interface {
 
-	
+
 	// lone comment
 
 
 }
-
-
-
 -- foo.go.golden --
 package p