[nautilus] README: Clarify supported version

[Carlos Soriano <csoriano src gnome org>]

commit c2d16ddd779575e2a31fd733b210d4f6129b7633
Author: Carlos Soriano <csoriano1618 gmail com>
Date:   Mon Dec 17 15:17:02 2018 +0000

    README: Clarify supported version

 README.md | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/README.md b/README.md
index a044f63f6..7e75b03d0 100644
--- a/README.md
+++ b/README.md
@@ -7,6 +7,9 @@
 This is [Nautilus](https://wiki.gnome.org/Apps/Nautilus), the file manager for
 GNOME.
 
+## Supported version
+Only latest Nautilus version 3.30 as provided upstream is supported. Try out the [Flatpak 
nightly](https://wiki.gnome.org/Apps/Nightly) installation before filling issues to ensure the installation 
is reproducible and doesn't have downstream changes on it. In case you cannnot reproduce in the nightly 
installation, don't hesitate to file an issue in your distribution.
+
 ## Hacking on Nautilus
 
 To build the development version of Nautilus and hack on the code