chore(cli): improve documentation for scan command.

cli/src/commands/scan.rs

@@ -22,14 +22,15 @@ use crate::{help, walk};
 pub fn scan() -> Command {
     super::command("scan")
         .about("Scan a file or directory")
+        .long_about(help::SCAN_LONG_HELP)
         .arg(
             arg!(<RULES_PATH>)
-                .help("Path to YARA source file")
+                .help("Path to a YARA source file or directory")
                 .value_parser(value_parser!(PathBuf))
                 .action(ArgAction::Append)
         )
         .arg(
-            arg!(<PATH>)
+            arg!(<TARGET_PATH>)
                 .help("Path to the file or directory that will be scanned")
                 .value_parser(value_parser!(PathBuf))
         )
@@ -94,7 +95,7 @@ pub fn scan() -> Command {
 
 pub fn exec_scan(args: &ArgMatches) -> anyhow::Result<()> {
     let mut rules_path = args.get_many::<PathBuf>("RULES_PATH").unwrap();
-    let path = args.get_one::<PathBuf>("PATH").unwrap();
+    let target_path = args.get_one::<PathBuf>("TARGET_PATH").unwrap();
     let compiled_rules = args.get_flag("compiled-rules");
     let num_threads = args.get_one::<u8>("threads");
     let path_as_namespace = args.get_flag("path-as-namespace");
@@ -162,7 +163,7 @@ pub fn exec_scan(args: &ArgMatches) -> anyhow::Result<()> {
     let state = ScanState::new(start_time);
 
     w.walk(
-        path,
+        target_path,
         state,
         // Initialization
         |_, output| {

cli/src/help.rs

@@ -69,3 +69,17 @@ Examples:
 yr completion bash > $(brew --prefix)/etc/bash_completion.d/yr
 yr completion zsh > "${fpath[1]}/_kubectl"
 "#;
+
+pub const SCAN_LONG_HELP: &str = r#"Scan a file or directory
+
+<RULES_PATH> can be the path to a file containing YARA rules, or the path to a directory
+containing *.yar or *.yara files. When <RULES_PATH> is a directory, it will be traversed 
+recursively looking for rule files. Multiple <RULES_PATH> can be specified.
+
+<TARGET_PATH> is the file or directory that will be scanned.
+
+Examples:
+
+yr scan rules_file.yar scanned_file
+yr scan rules_dir scanned_file
+"#;