Add help argument

src/main.rs

@@ -13,6 +13,7 @@ enum Mode {
     Single(String),
     TerminateByPid(u32),
     TerminateByName(String),
+    Help,
 }
 
 // pkill                 => all unique processed, excl. svchost
@@ -88,6 +89,18 @@ fn main() -> ExitCode {
                 ExitCode::FAILURE
             }
         }
+        Mode::Help => {
+            let lines = [
+                "pkill                     => all unique processed, excl. system\n",
+                "pkill <name>              => filtered processes by name or it's part\n",
+                "pkill --all               => all processes, incl. system\n",
+                "pkill --pid <name>        => PID of the first occurence\n",
+                "pkill --kill <PID>/<name> => terminate process by its PID or name\n",
+                "pkill --help              => print help\n",
+            ];
+            println!("{}", lines.concat());
+            ExitCode::SUCCESS
+        }
     }
 }
 
@@ -96,6 +109,7 @@ fn parse_mode() -> Mode {
     let mut iter = env::args().skip(1).into_iter();
     while let Some(el) = iter.next() {
         match el.as_str() {
+            "--help" => mode = Mode::Help,
             "--all" => {
                 mode = Mode::All;
             }