[PATCH] Document update for nd/unpack-trees-with-cache-tree

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Fix an incorrect comment in the new code added in b4da37380b
(unpack-trees: optimize walking same trees with cache-tree -
2018-08-18) and document about the new test variable that is enabled
by default in test-lib.sh in 4592e6080f (cache-tree: verify valid
cache-tree in the test suite - 2018-08-18)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 On top of nd/unpack-trees-with-cache-tree. Incremental update since
 this topic has entered 'next'

 t/README       | 4 ++++
 unpack-trees.c | 4 ++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/t/README b/t/README
index 8373a27fea..0e7cc23734 100644
--- a/t/README
+++ b/t/README
@@ -315,6 +315,10 @@ packs on demand. This normally only happens when the object size is
 over 2GB. This variable forces the code path on any object larger than
 <n> bytes.
 
+GIT_TEST_VALIDATE_INDEX_CACHE_ENTRIES=<boolean> checks that cache-tree
+records are valid when the index is written out or after a merge. This
+is mostly to catch missing invalidation. Default is true.
+
 Naming Tests
 ------------
 
diff --git a/unpack-trees.c b/unpack-trees.c
index 3394540842..5a18f36143 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -676,8 +676,8 @@ static int index_pos_by_traverse_info(struct name_entry *names,
 
 /*
  * Fast path if we detect that all trees are the same as cache-tree at this
- * path. We'll walk these trees recursively using cache-tree/index instead of
- * ODB since already know what these trees contain.
+ * path. We'll walk these trees in an iteractive loop using cache-tree/index
+ * instead of ODB since already know what these trees contain.
  */
 static int traverse_by_cache_tree(int pos, int nr_entries, int nr_names,
 				  struct name_entry *names,
-- 
2.19.0.rc0.337.ge906d732e7