README: Give examples of the different kinds of Provides

#14

README.md

@@ -27,17 +27,23 @@ from your Tox configuration.
 (As far as we know, this is required in order to have individual environments
 show up as separate runs on GitHub. Discuss this limitation in [issue 8].)
 
-Optionally, you can install RPM packages from Fedora by setting the
-`dnf_install` to a space separated list of packages (or provides, groups etc.,
-the string will be literally used in `dnf install ...`):
+You can also install RPM packages from Fedora by setting `dnf_install` to
+a space-separated list of *provides*, such as:
+
+* Fedora package names, e.g. `libgit2-devel`,
+* pkgconfig names, e.g. `pkgconfig(libffi)`,
+* commands, e.g. `/usr/bin/cowsay`, ...
 
 ```yaml
 - uses: fedora-python/tox-github-action
   with:
     tox_env: py38
-    dnf_install: libffi-devel libyaml-devel
+    dnf_install: pkgconfig(libffi) libgit2-devel
 ```
 
+The string will be literally used in `dnf install ...`, so you can also use
+groups or DNF options.
+
 [issue 8]: https://github.com/fedora-python/tox-github-action/issues/8
 
 ## License