Add a few comments

Author: Kobzol

src/tools/run-make-support/src/command.rs

@@ -4,6 +4,9 @@ use std::io::Write;
 use std::ops::{Deref, DerefMut};
 use std::process::{Command as StdCommand, ExitStatus, Output, Stdio};
 
+/// This is a custom command wrapper that simplifies working with commands
+/// and makes it easier to ensure that we check the exit status of executed
+/// processes.
 #[derive(Debug)]
 pub struct Command {
     cmd: StdCommand,
@@ -83,6 +86,8 @@ impl DerefMut for Command {
 }
 
 /// Represents the result of an executed process.
+/// The various `assert_` helper methods should preferably be used for
+/// checking the contents of stdout/stderr.
 pub struct CompletedProcess {
     output: Output,
 }