README.md: remove message about unsupported Snap/Flatpak

And add steps to fix issues caused by Snap/Flatpak to TROUBLESHOOTING.md
just in case. Solution found by Tyalie, wording/mistakes authored by
yours truly.

Closes #1591

README.md

@@ -14,9 +14,7 @@ Just click on any textarea and it will be immediately replaced by an instance of
 
 Before installing anything please read [SECURITY.md](SECURITY.md) and make sure you're okay with everything mentioned. In the event you think of a way to compromise Firenvim, please send me an email (you can find my address in my commits).
 
-1. Make sure you are using [Neovim][nvim] 0.6.0 or later. This plugin will not work with vanilla [VIM][vim] or [Vimr][vimr]. Also make sure that your browser hasn't been installed with Snap or Flatpak - these prevent Firenvim from starting Neovim.
-
-2. Install Firenvim as a VIM plugin as you would any other, then run the built-in post-install script.
+1. Install Firenvim as a regular NeoVim plugin, then run the built-in post-install script.
 
     * [packer](https://github.com/wbthomason/packer.nvim)
 
@@ -70,7 +68,7 @@ Before installing anything please read [SECURITY.md](SECURITY.md) and make sure
         $ nvim --headless "+call firenvim#install(0) | q"
         ```
 
-3. Finally, install the Firenvim addon for your browser from [Mozilla's store](https://addons.mozilla.org/en-US/firefox/addon/firenvim/) or [Google's](https://chrome.google.com/webstore/detail/firenvim/egpjdkipkomnmjhjmdamaniclmdlobbo).
+2. Install the Firenvim addon for your browser from [Mozilla's store](https://addons.mozilla.org/en-US/firefox/addon/firenvim/) or [Google's](https://chrome.google.com/webstore/detail/firenvim/egpjdkipkomnmjhjmdamaniclmdlobbo).
 
 If you would rather build and install Firenvim from source, check [CONTRIBUTING.md](CONTRIBUTING.md).
 

TROUBLESHOOTING.md

@@ -1,6 +1,16 @@
 # Troubleshooting Firenvim
 
-If you're having issues with Firenvim, here are the following steps you can take in order to check if everything is correctly set up on your side:
+If you're having issues with Firenvim, here are the steps you can take in order to check if everything is correctly set up on your side.
+
+## Make sure Flatpak and Snap are not preventing Firenvim from working
+
+If your browser is installed through Snap or Flatpak, sandboxing mechanisms might be preventing the browser from starting Neovim. You can confirm this by running:
+
+```
+flatpak permissions webextensions
+```
+
+If the output of this command shows that Snap/Flatpak are preventing Firenvim from running, you need to run `flatpak permission-set webextensions firenvim snap.firefox yes` to change that.
 
 ## Make sure the neovim plugin is installed