update doc to clarify the behavior when removing key/value pair durin…

…g iteration

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

README.md

@@ -445,6 +445,11 @@ When you have iterated to the end of the cursor then `Next()` will return a
 before calling `Next()` or `Prev()`. If you do not seek to a position then
 these functions will return a `nil` key.
 
+If you remove key/value pairs during iteration, the cursor may automatically
+move to the next position if present in current node each time removing a key.
+When you call `c.Next()` after removing a key, it may skip one key/value pair.  
+Refer to [pull/611](https://github.com/etcd-io/bbolt/pull/611) to get more detailed info.
+
 During iteration, if the key is non-`nil` but the value is `nil`, that means
 the key refers to a bucket rather than a value.  Use `Bucket.Bucket()` to
 access the sub-bucket.
@@ -869,6 +874,12 @@ Here are a few things to note when evaluating and using Bolt:
   to grow. However, it's important to note that deleting large chunks of data
   will not allow you to reclaim that space on disk.
 
+* Removing key/values pairs in a bucket during iteration on the bucket using
+  cursor may not work properly. Each time when removing a key/value pair, the
+  cursor may automatically move to the next position if present. When users
+  call `c.Next()` after removing a key, it may skip one key/value pair.
+  Refer to https://github.com/etcd-io/bbolt/pull/611 for more detailed info.
+
   For more information on page allocation, [see this comment][page-allocation].
 
 [page-allocation]: https://github.com/boltdb/bolt/issues/308#issuecomment-74811638