Add instructions for Red Hat-based distributions

The package names on Red Hat distributions (e.g., Fedora, CentOS) are
less obvious. Adding this to the README may help some users. This was
tested on Fedora 32, but is probably similar for CentOS.

README.md

@@ -13,6 +13,12 @@ distributions, execute the following command:
 sudo apt-get install libudev-dev
 ```
 
+For Red Hat distributions (e.g. Fedora):
+
+```
+sudo dnf install systemd-devel
+```
+
 `libudev` is a Linux-specific package. It is not available for Windows, OSX, or other operating
 systems.