Improve README (#4, #6)

README.md

@@ -1,7 +1,8 @@
 # ipynb-quicklook
 
-**Note**: This plugin has now been integrated into a native macOS app,
-[Jupyter Notebook Viewer](https://github.com/tuxu/nbviewer-app).
+**Note**: This plugin has now been integrated into a native macOS app, [Jupyter
+Notebook Viewer](https://github.com/tuxu/nbviewer-app). This is the recommended
+way to install the QuickLook generator and simplifies installation.
 
 A stand-alone [Quick Look](https://en.wikipedia.org/wiki/Quick_Look) generator
 for [Jupyter](https://jupyter.org/)/[IPython](https://ipython.org/) notebooks on
@@ -12,10 +13,20 @@ macOS. Contents are rendered on-the-fly using
 
 - Download `ipynb-quicklook.qlgenerator`
   ([Releases](https://github.com/tuxu/ipynb-quicklook/releases))
-- Move the generator into `/Library/QuickLook`. You may need to run `qlmanage
+- The generator is unsigned and not notarized by Apple. You need to remove the
+  quarantine attribute like this on macOS Catalina and later 
+  ([#6](https://github.com/tuxu/ipynb-quicklook/issues/6)):
+  ```sh
+  xattr -d com.apple.quarantine ipynb-quicklook.qlgenerator
+  ```
+- Move the generator into `/Library/QuickLook` [^1]. You may need to run `qlmanage
   -r` to reset the Quick Look server and caches.
 - Press <kbd>space</kbd> whenever you encounter a `.ipynb` file. Enjoy 👍
 
+[^1]: Note that the generator must be installed globally. Installation to
+  `~/Library/QuickLook/` is not sufficient (see
+  [#4](https://github.com/tuxu/ipynb-quicklook/issues/4)).
+
 ## Similar projects
 
 - [jupyter-notebook-quick-look](https://github.com/jendas1/jupyter-notebook-quick-look):
@@ -30,4 +41,4 @@ macOS. Contents are rendered on-the-fly using
 This project is licensed under the MIT license. See [LICENSE.md](LICENSE.md) for
 details.
 
-© 2017 [Tino Wagner](http://www.tinowagner.com/)
+© 2017 [Tino Wagner](http://www.tinowagner.com/)