[#29] Update Unix trail

* Formatt Unix trail as other trails.
* Add recommended chapters for "The Linux Programming Interface".

trails/unix.md

@@ -1,30 +1,43 @@
 Unix
-----
+====
 
-* Read [The Linux Programming Interface](http://www.amazon.com/The-Linux-Programming-Interface-Handbook/dp/1593272200). ($)
-* Refer to these man pages often:
+Critical learning
+-----------------
+
+* Read [The Linux Programming Interface](http://www.amazon.com/The-Linux-Programming-Interface-Handbook/dp/1593272200) Chapters 1,2,6,8,10,14,15,18,25,44,62. ($)
+
+Validation
+----------
+
+You know everyday Unix when you routinely use the following:
 
 ```shell
-man ack
-man awk
-man cat
-man chmod
-man chown
-man cp
-man export
-man find
-man kill
-man locate
-man ls
-man mkdir
-man mv
-man ps
-man rm
-man sed
-man sort
-man tail
-man top
-man vim
-man whereis
-man xargs
+ack
+awk
+cat
+chmod
+chown
+cp
+export
+find
+kill
+locate
+ls
+mkdir
+mv
+ps
+rm
+sed
+sort
+tail
+top
+vim
+whereis
+xargs
 ```
+
+Ongoing reference
+-----------------
+
+For each command, refer to the man pages often:
+man <command>