entc: improve generated comments for edges and fields (#2632)

* replace default field comment with user comment if defined
* use comments defined on edges in generated entities
* add docs for comment method on edges and fields
* update integration to reflect above changes

doc/md/schema-edges.mdx

@@ -1416,6 +1416,23 @@ However, you should note, that this is currently an SQL-only feature.
 
 Read more about this in the [Indexes](schema-indexes.md) section.
 
+## Comments
+
+A comment can be added to the edge using the `.Comment()` method. This comment
+appears before the edge in the generated entity code. Newlines are supported 
+using the `\n` escape sequence.
+
+```go
+// Edges of the User.
+func (User) Edges() []ent.Edge {
+	return []ent.Edge{
+		edge.To("pets", Pet.Type).
+			Comment("Pets that this user is responsible for taking care of.\n" + 
+				"May be zero to many, depending on the user.")
+	}
+}
+```
+
 ## Annotations
 
 `Annotations` is used to attach arbitrary metadata to the edge object in code generation.

doc/md/schema-fields.md

@@ -508,6 +508,23 @@ func (User) Fields() []ent.Field {
 }
 ```
 
+## Comments
+
+A comment can be added to a field using the `.Comment()` method. This comment
+appears before the field in the generated entity code. Newlines are supported 
+using the `\n` escape sequence.
+
+```go
+// Fields of the user.
+func (User) Fields() []ent.Field {
+	return []ent.Field{
+		field.String("name").
+			Default("John Doe").
+			Comment("Name of the user.\n If not specified, defaults to \"John Doe\"."),
+	}
+}
+```
+
 ## Storage Key
 
 Custom storage name can be configured using the `StorageKey` method.