Add file summaries

src/main.rs

@@ -6,7 +6,13 @@
     You should have received a copy of the GNU General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
+/*
+    main.rs
+    This file contains the primary logic of the application
+*/
+
 mod pacman_install_check;
+mod shell_commands;
 
 fn main() {
     println!("{}", copyright_notice());

src/pacman_install_check.rs

@@ -6,6 +6,11 @@
     You should have received a copy of the GNU General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
+/*
+    pacman_install_check.rs
+    This file contains a method to check if the pacman package manager is installed
+*/
+
 use std::fmt;
 use std::fmt::Formatter;
 use std::path::Path;