download: add note in mac os install about granting security exception

Author: clintonsteiner

_site/download.html

@@ -316,6 +316,7 @@ <h3 id="macos">
     <div class="downloadNotesDiv">
       <p>
         The macOS version is <strong>barely supported,</strong> because we don't have active macOS developers/contributors.<br>
+        To install, you'll need to grant an exception via the Open Anyway button in Privacy and Security settings.<br>
         The project is in need of macOS developers. If you are a macOS developer willing to help, just go to our bug tracker for a list of macOS related issues. Or try to fix bugs that you yourself have discovered and annoy you.
       </p>
     </div>

src/download.liquid

@@ -314,6 +314,7 @@ src:
     <div class="downloadNotesDiv">
       <p>
         The macOS version is <strong>barely supported,</strong> because we don't have active macOS developers/contributors.<br>
+        To install, you'll need to grant an exception via the Open Anyway button in Privacy and Security settings.<br>
         The project is in need of macOS developers. If you are a macOS developer willing to help, just go to our bug tracker for a list of macOS related issues. Or try to fix bugs that you yourself have discovered and annoy you.
       </p>
     </div>