AWS ES 2.x snapshot status endpoint failure

Document that this does not work.

README.rst

@@ -15,7 +15,7 @@ Compatibility Matrix
 +--------+----------+------------+----------+------------+----------+
 |Version | ES 1.x   | AWS ES 1.x | ES 2.x   | AWS ES 2.x | ES 5.x   |
 +========+==========+============+==========+============+==========+
-|    3   |    yes   |     yes    |   yes    |     yes    |   no     |
+|    3   |    yes   |     yes    |   yes    |     yes*   |   no     |
 +--------+----------+------------+----------+------------+----------+
 |    4   |    no    |     no     |   yes    |     no     |   yes    |
 +--------+----------+------------+----------+------------+----------+
@@ -38,6 +38,8 @@ It is also important to note that Curator 4 requires access to the
 support this endpoint (such as AWS ES, see #717) *will not* be able to use
 Curator version 4.
 
+\* It appears that AWS ES 2.x (not confirmed for 1.x) [does not allow access to the snapshot status endpoint](https://github.com/elastic/curator/issues/796).  This prevents Curator 3 from being used to make snapshots.
+
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