add unlink example

Author: Vladimir Kotal

user-access.tex

@@ -253,7 +253,7 @@
 a file.  See the example below.  \emsl{Unix systems do not have delete-like
 operation for a file}, the file is deleted automatically once it is no longer
 referenced from a directory structure and the file is not presently open by any
-process.
+process (see \example{unlink/unlink.c}).
 
 \begin{verbatim}
 $ whoami
@@ -263,9 +263,9 @@
 $ ls -l janp-dir
 total 0
 -rw-r--r--   1 root  root     0 Mar 23 12:11 root_wuz_here.txt
-$ rm janp-dir/root_wuz_here.txt 
+$ rm janp-dir/root_wuz_here.txt
 rm: janp-dir/root_wuz_here.txt: override protection 644 (yes/no)? yes
-$ ls janp-dir/root_wuz_here.txt 
+$ ls janp-dir/root_wuz_here.txt
 janp-dir/root_wuz_here.txt: No such file or directory
 \end{verbatim}