fix: follow symlinks when grepping for desktop entries

[cluther]

Thank you for writing linkquisition. It's such a great default browser
replacement for those of us that like to use different browsers and profiles
for different purposes. It does just what I need, and no more. I hope you find
this pull request acceptable. It's a small thing, but needed for those who have
symlinks within their $XDG_DATA_DIRS paths. I don't know how common that is,
but it at least affects people installing browsers with Nix home-manager.

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When running browsers installed via the Nix home-manager, the browser
.desktop files will be found within ~/.nix-profile/share/applications/
and ~/.nix-profile/share will be in $XDG_DATA_DIRS. The
~/.nix-profile/share directory is a symlink, and grep -r will follow
that successfully, but then the applications/firefox.desktop within
will also be a symlink. A grep -r won't follow that, so we have to use
grep -R to follow all symlinks to actually find the desktop entries.

For example, without this fix, I see the following when running
linkquisition https://google.com.

failed to call grep for determining a .desktop entry for firefox -P Personal --class=firefox-personal %U: exit status 1
failed to call grep for determining a .desktop entry for google-chrome-stable --user-data-dir="/home/cluther/.config/google-chrome-personal" %U: exit status 1

With this change, linkquisition is able to auto-detect all of the
browser entries I have, and launch into them without error.