Clarify write usage in comment for /dev/chardev

The original comment referred to /dev/hello, but the actual device
created by the module is /dev/chardev.

In addition, writing to /dev/chardev using output redirection (>)
typically fails due to insufficient permissions, since redirection is
handled by the shell before sudo applies. As a result, the
device_write() function may never be entered.

This change updates the comment to recommend using a pipe with
`sudo tee`, which correctly elevates privileges and allows the write
operation to reach the driver.

Author: chmh0624

examples/chardev.c

@@ -152,7 +152,7 @@ static ssize_t device_read(struct file *filp, /* see include/linux/fs.h   */
     return bytes_read;
 }
 
-/* Called when a process writes to dev file: echo "hi" > /dev/hello */
+/* Called when a process writes to dev file: echo "hi" | sudo tee /dev/chardev */
 static ssize_t device_write(struct file *filp, const char __user *buff,
                             size_t len, loff_t *off)
 {