Add Linux Users page contents

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linux/usage/users.md

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 # Linux users
+
+User management in Raspbian is done on the command line. The default user is `pi` with the password `raspberry`. You can add users and change each user's password.
+
+## Change your password
+
+When logged in as the `pi` user you can change your password with the `passwd` command.
+
+Enter `passwd` on the command line and hit `Enter`. You'll be prompted to enter your current password to authenticate, and then asked for a new password. Hit `Enter` on completion and you'll be asked to confirm it. Note that no characters will be displayed while entering your password. Once you've correctly confirmed, you'll be shown a success message and the new password will be in effect immediately.
+
+If your user has sudo permissions, you can change another user's password with `passwd` proceeded by the user's username, e.g. `passwd bob` will allow you to set the user `bob`'s password.
+
+### Remove a user's password
+
+You can remove the password for the user `bob` with `passwd bob -d`.
+
+## Create a new user
+
+You can create additional users on your Raspbian installation with the `useradd` command.
+
+Enter `useradd bob` and you'll be prompted for a password for the new user `bob`. Leave blank for no password.
+
+### Home folder
+
+When you create a new user, they will have a home folder in `/home/`. The `pi` user's home folder is at `/home/pi/`.
+
+#### skel
+
+Upon creating a new user, the contents of `/etc/skel/` will be copied to the new user's home folder. You can add or modify dotfiles such as the `.bashrc` in `/etc/skel/` to your taste and this version will be applied to new users created.
+
+## Sudoers
+
+The default `pi` user on Raspbian is a sudoer. This gives the abiliy to run commands as root when preceeded by `sudo`, and to switch to the root user with `sudo su`.
+
+To add a new user to sudoers, type `sudo visudo` (from a sudoer user) and find the line `root    ALL=(ALL:ALL) ALL`, found under the commented header '# User privilege specification'. This will prompt you for a default editor the first time you run it (if you don't have a preference, try Nano). Copy this line and switch from `root` to the username. To allow passwordless root access, change to `NOPASSWD: ALL`. The example below gives the user `bob` passwordless sudo access:
+
+```bash
+# User privilege specification                                                  
+root    ALL=(ALL:ALL) ALL                                                       
+bob ALL = NOPASSWD: ALL
+```
+
+Save and exit to apply the changes. **Be careful**
+
+## Delete a user
+
+You can delete a user on your system with the command `userdel`. Apply the `-r` flag to remove their home folder too:
+
+```bash
+userdel -r bob
+```