Rollup merge of #36841 - GuillaumeGomez:process_doc, r=steveklabnik

Improve process module doc a bit

r? @steveklabnik

src/libstd/process.rs

@@ -8,7 +8,25 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Working with processes.
+//! A module for working with processes.
+//!
+//! # Examples
+//!
+//! Basic usage where we try to execute the `cat` shell command:
+//!
+//! ```should_panic
+//! use std::process::Command;
+//!
+//! let mut child = Command::new("/bin/cat")
+//!                         .arg("file.txt")
+//!                         .spawn()
+//!                         .expect("failed to execute child");
+//!
+//! let ecode = child.wait()
+//!                  .expect("failed to wait on child");
+//!
+//! assert!(ecode.success());
+//! ```
 
 #![stable(feature = "process", since = "1.0.0")]