Update kernel header install command for clarity

Remove the redundant 'kmod' installation since it is already
installed earlier. Also replace the hardcoded kernel version
with 'uname -r' to improve portability and compatibility with
modern Linux distributions.

lkmpg.tex

@@ -210,7 +210,7 @@ apt-cache search linux-headers-`uname -r`
 The following command provides information on the available kernel header files.
 Then for example:
 \begin{codebash}
-sudo apt-get install kmod linux-headers-5.4.0-80-generic
+sudo apt-get install linux-headers-`uname -r`
 \end{codebash}
 
 On Arch Linux: