Update README.md with information re: v1.00.0-190618 release issues

On Monday, June 17th 2019 we released version 1.00.0-190618 which unfortunately has a few issues which occur on certain configurations that were not
caught by our internal testing processes. Because automatic updates were enabled by default on new installations, this has caused instances where servers
have become unavailable due to the upgrade failing and we sincerely apologize for any inconvenience and disruption.

If you have experienced a failed upgrade, please submit an issue report via GitHub Issues. We are planning on shipping the v1.0.1 hotfix release once we
have validated that it corrects the issues which we have been made aware of and other bugs that we've fixed since its release.

README.md

@@ -1,6 +1,15 @@
 [Hestia Control Panel](https://www.hestiacp.com/)
 ==================================================
 
+**Important notice regarding v1.00.0-190618 release**
+----------------------------
+On Monday, June 17th 2019 we released version 1.00.0-190618 which unfortunately has a few issues which occur on certain configurations that were not
+caught by our internal testing processes. Because automatic updates were enabled by default on new installations, this has caused instances where servers
+have become unavailable due to the upgrade failing and we sincerely apologize for any inconvenience and disruption.
+
+If you have experienced a failed upgrade, please submit an issue report via GitHub Issues. We are planning on shipping the v1.0.1 hotfix release once we
+have validated that it corrects the issues which we have been made aware of and other bugs that we've fixed between the time of the initial release and now.
+
 **Pre-Release Software Information**
 ----------------------------
 **Hestia Control Panel is undergoing rapid changes in development. As such, it is important to note that:**