Update source/faq/indexes.txt

totalIndexSizes shows the sum of index sizes on a collection, not the sizes of each individual index. Collection stats shows the index sizes broken out.

Author: Richard Kreuter

source/faq/indexes.txt

@@ -39,7 +39,7 @@ To list a collection's indexes, use the
 How do you determine the size of an index?
 ------------------------------------------
 
-To check index size, use :method:`db.collection.totalIndexSize()`.
+To check the sizes of the indexes on a collection, use :method:`db.collection.stats()`.
 
 .. todo:: FAQ How do I determine if an index fits into RAM?