update macos instructions

cert_instructions/macosx_cert.md

@@ -1,10 +1,12 @@
   * Login to your Bubble
   * Go to "Devices"
   * In the "Download Certificate" section, click "Mac OS X"
-  * In the file dialog, choose "Open With" and open with the app "Keychain Access"
-  * In the "Keychain Access" app, select "Certificates" from the "Category" list in the bottom left corner.
-  * Select the Certificate you just downloaded, it's name is the same as your Bubble's name
-  * Right-click on the Certificate and choose "Get Info"
+  * In the file dialog, choose "Save File"
+  * Open the "Keychain Access" app
+  * Select the "System" keychain from the "Keychains" list in the top-left panel
+  * From the "File" menu, choose "Import Items..."
+  * Find the Certificate file that you downloaded earlier and click "Open"
+  * Right-click on the Certificate that you just added and choose "Get Info"
   * Toggle the arrow next to the "Trust" section to expand it
   * In the top drop-down box which reads "When using this certificate:", select "Always Trust"
   * Close the Certificate info dialog