Update README.md

Add warning to README.md that keys and values in `ForEach()` are
invalid outside of transaction.

1 files changed, 4 insertions, 0 deletions

diff --git a/README.md b/README.md
index 0d3b4bd..2a69d95 100644
--- a/README.md
+++ b/README.md
@@ -448,6 +448,10 @@ db.View(func(tx *bolt.Tx) error {
 })
 ```
 
+Please note that keys and values in `ForEach()` are only valid while
+the transaction is open. If you need to use a key or value outside of
+the transaction, you must use `copy()` to copy it to another byte
+slice.
 
 ### Nested buckets