Typo in `du -hk *` for summary

`du -hk` means `du -k`, last option wins since both of them set display unit. I think, you mean `du -hs *` for summary.

README.md

@@ -60,7 +60,7 @@ Notes:
 
 - Know `ssh`, and the basics of passwordless authentication, via `ssh-agent`, `ssh-add`, etc.
 
-- Basic file management: `ls` and `ls -l` (in particular, learn what every column in `ls -l` means), `less`, `head`, `tail` and `tail -f` (or even better, `less +F`), `ln` and `ln -s` (learn the differences and advantages of hard versus soft links), `chown`, `chmod`, `du` (for a quick summary of disk usage: `du -hk *`). For filesystem management, `df`, `mount`, `fdisk`, `mkfs`, `lsblk`.
+- Basic file management: `ls` and `ls -l` (in particular, learn what every column in `ls -l` means), `less`, `head`, `tail` and `tail -f` (or even better, `less +F`), `ln` and `ln -s` (learn the differences and advantages of hard versus soft links), `chown`, `chmod`, `du` (for a quick summary of disk usage: `du -hs *`). For filesystem management, `df`, `mount`, `fdisk`, `mkfs`, `lsblk`.
 
 - Basic network management: `ip` or `ifconfig`, `dig`.