Add explanatory note to crypto/store/README

Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/crypto/store/README b/crypto/store/README
index 966168f..3d259c6 100644
--- a/crypto/store/README
+++ b/crypto/store/README
@@ -1,3 +1,9 @@
+NOTE:
+	This is a planned replacement for X509_STORE.
+	It is incomplete, has compile errors, and is
+	not built as part of the standard configuration.
+
+
 The STORE type
 ==============