Fix bikeshed indentation error

Also removes some extra trailing whitespace on a line.

index.bs

@@ -700,12 +700,12 @@ If your feature does **anything**
 that falls into the
 following categories:
 * Interacts with a document from the "outside"
-  (e.g. sends information to a document)
+    (e.g. sends information to a document)
 * Makes cross-document interaction/resource sharing possible
-  (e.g. holding locks)
+    (e.g. holding locks)
 * May malfunction when a document is
-  kept in a non-[=Document/fully active=] BFCached state
-  (instead of getting destroyed)
+    kept in a non-[=Document/fully active=] BFCached state
+    (instead of getting destroyed)
     after the user navigates away from it
     or gets restored
     (e.g. expects that a state saved in the document
@@ -714,7 +714,7 @@ following categories:
 Specify how your feature works
 with non-[=Document/fully active=] BFCached documents,
 following the guidelines in the
-[Supporting BFCached Documents](https://w3ctag.github.io/bfcache-guide/) guide.  
+[Supporting BFCached Documents](https://w3ctag.github.io/bfcache-guide/) guide.
 
 Note: It is possible for a document
 to become non-[=Document/fully active=]