Preps for 1.7.0 release

Update version fields for 1.7.0 release.
Added compatibility note for zephyr-rtos.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/README.md b/README.md
index 94bda52..bda8cf8 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 [travis]: https://travis-ci.org/mcu-tools/mcuboot
 [license]: https://github.com/mcu-tools/mcuboot/blob/master/LICENSE
 
-This is mcuboot version 1.7.0-rc2
+This is mcuboot version 1.7.0
 
 MCUboot is a secure bootloader for 32-bit MCUs. The goal of MCUboot is to
 define a common infrastructure for the bootloader, system flash layout on