Update README.md

Author: cdaniel

README.md

@@ -14,3 +14,7 @@ The code is licenced under creative commons (CC-BY-SA), except the LEF logo (atl
 This is a community based project. Any help is really appreciated. Read [here](https://github.com/cdaniel/atlas2/wiki/Contributing) how to contribute.
 
 [Set up for developers](https://github.com/cdaniel/atlas2/wiki/Dev-Setup)
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+# Notice:
+Read [release info](https://github.com/cdaniel/atlas2/releases) before updating existing tool. Before upgrading to latest version, backup your data first!