Add sudo for file access permissions

Add sudo to commands in Chapter 8 for example module interaction.

The "myvariables" in the module are set with 0660 permissions
via __ATTR(), preventing direct user access.

Options to fix this:
1. Instruct users to use 'sudo' to read/write files.
2. Relax the permission settings to 0666.

This commit adopts the sudo method to maintain security constraints.

lkmpg.tex

@@ -1347,14 +1347,14 @@ \section{sysfs: Interacting with your module}
 What is the current value of \cpp|myvariable| ?
 
 \begin{codebash}
-cat /sys/kernel/mymodule/myvariable
+sudo cat /sys/kernel/mymodule/myvariable
 \end{codebash}
 
 Set the value of \cpp|myvariable| and check that it changed.
 
 \begin{codebash}
-echo "32" > /sys/kernel/mymodule/myvariable
-cat /sys/kernel/mymodule/myvariable
+echo "32" | sudo tee /sys/kernel/mymodule/myvariable
+sudo cat /sys/kernel/mymodule/myvariable
 \end{codebash}
 
 Finally, remove the test module: