Add note for Windows users clicking through the security dialog

Covers Windows users for now, until code signing becomes
more reasonable: #17

.github/docs/download-app.md

@@ -11,3 +11,14 @@ For more information, see the [latest release][].
 
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 <img src="https://analytics.johnstarich.com/matomo.php?idsite=2&amp;rec=1&amp;action_name=Download+App" style="border:0" alt="" />
+
+**Windows users:**
+
+When downloading, you will see a possible malware warning because [code signing costs a bit][windows-signing] 😔.
+To bypass the warning, choose "Keep" from the option menu.
+
+After opening, you will get an additional warning. To bypass the second warning, click "More info" in the top-left of the popup followed by "Run anyway".
+
+If you're a Sage Windows user, **please show your support by [commenting on this issue to add Windows code signing support][windows-signing]**.
+
+[windows-signing]: https://github.com/JohnStarich/sage/issues/17