apimachinery/pkg/runtime/doc: Split list into paragraphs

Godoc uses go/doc to convert comments to HTML [1], and go/doc has no
markup for lists [2].  With the previous comment, the lack of
paragraph-splitting lines between the list entries was leading to
entries 0, 1, etc. being formatted as a single paragraph.  And the
hanging indents for entry 3, etc. were leading to formatting within
<pre> blocks:

  $ curl -s https://godoc.org/k8s.io/apimachinery/pkg/runtime | grep -B1 -A7 'Your API objects'
  <p>
  0. Your API objects have a common metadata struct member, TypeMeta.
  1. Your code refers to an internal set of API objects.
  2. In a separate package, you have an external set of API objects.
  3. The external set is considered to be versioned, and no breaking
  </p>
  <pre>changes are ever made to it (fields may be added but not changed
  or removed).
  </pre>

[1]: https://godoc.org/golang.org/x/tools/cmd/godoc
[2]: https://golang.org/pkg/go/doc/#ToHTML

staging/src/k8s.io/apimachinery/pkg/runtime/doc.go

@@ -18,20 +18,27 @@ limitations under the License.
 // that follow the kubernetes API object conventions, which are:
 //
 // 0. Your API objects have a common metadata struct member, TypeMeta.
+//
 // 1. Your code refers to an internal set of API objects.
+//
 // 2. In a separate package, you have an external set of API objects.
+//
 // 3. The external set is considered to be versioned, and no breaking
-//    changes are ever made to it (fields may be added but not changed
-//    or removed).
+// changes are ever made to it (fields may be added but not changed
+// or removed).
+//
 // 4. As your api evolves, you'll make an additional versioned package
-//    with every major change.
+// with every major change.
+//
 // 5. Versioned packages have conversion functions which convert to
-//    and from the internal version.
+// and from the internal version.
+//
 // 6. You'll continue to support older versions according to your
-//    deprecation policy, and you can easily provide a program/library
-//    to update old versions into new versions because of 5.
+// deprecation policy, and you can easily provide a program/library
+// to update old versions into new versions because of 5.
+//
 // 7. All of your serializations and deserializations are handled in a
-//    centralized place.
+// centralized place.
 //
 // Package runtime provides a conversion helper to make 5 easy, and the
 // Encode/Decode/DecodeInto trio to accomplish 7. You can also register