Added userdel to linux
Added deluser page, related to userdel at #172
Added nohup page
Added usermod page
Adding a line for sed for making multiple replacements in one command.
tcpdump command to output to a dated filename all traffic not on port 22
adds two more use cases for git-push
Update git-log.md

adds the command for displaying a detailed git history of a particular file or folder
Added example of overwriting an existing link
add wall
change message to file
add env command
Add exiftool and one example
Expand git-diff page

Added:
  * `—names-only` option.
  * `—summary` option.
Add tree command docs.
Added mysqldump.md
Added example which displays the size in a human readable format.
README: Exilir client
Merge pull request #181 from Gubolin/master

add wall
Merge pull request #185 from naxoc/tree

Add tree command docs.