[epiphany] README: warn not to use flathub :(

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 8f26b7ff3b7d4cec5c752bc00cae7c8e8c8b0ce4
Author: Michael Catanzaro <mcatanzaro posteo net>
Date:   Mon Aug 13 17:23:34 2018 +0000

    README: warn not to use flathub :(

 README.md | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/README.md b/README.md
index 3b86c2845..82f736ccf 100644
--- a/README.md
+++ b/README.md
@@ -10,8 +10,10 @@ Epiphany is opinionated.
 Epiphany is designed for Linux systems. The recommended way to install Epiphany
 is via [Flatpak](https://www.flatpak.org/). You may:
 
- * [Download the latest stable version from 
Flathub](https://flathub.org/repo/appstream/org.gnome.Epiphany.flatpakref)
-   (recommended); or
+ * ~~[Download the latest stable version from 
Flathub](https://flathub.org/repo/appstream/org.gnome.Epiphany.flatpakref)
+   (recommended).~~ Flathub downloads are currently not recommended due to major
+   security problems discovered in the application runtime. We expect this
+   situation to be improved in the future. In the meantime, do not use.
  * [Download Epiphany Technology Preview](https://webkitgtk.org/epiphany-tech-preview)
    if you are adventurous and want to help test tomorrow's Epiphany today. It
    is **not stable**.