Update passwordless.md

Following these instructions using Unbuntu 13.10 as client I had error "Agent admitted failure to sign using the key." Adding my RSA or DSA identities to the authentication agent, ssh-agent 
the execute the following command seems to have fixed this:  
```
ssh-add
```
Clearing partition table allows writing to a used SD card.

A "dd" on MacOS can fail due to lack of write permissions on the disk device, even when using sudo. This is a measure to protect SD cards from accidental overwritting. Clear the partition table on the SD card. This also sets the disk device permissions to allow writes.
Change to using Minecraft Pi from apt
Add Minecraft desktop logo
Remove old terminal image
Merge pull request #120 from gbaman/patch-1

Switch from using wget to installing via apt-get
Add notes about old/new installation instructions
Merge pull request #101 from jsavage/patch-1

Add ssh-add to passwordless ssh
Remove python-minecraftpi as it's a dependency

As per #120
Merge pull request #111 from vk5tu/patch-1

Clearing partition table allows writing to a used SD card.
New NOOBS v1.3.10 details
Update Raspbian image name
Update Raspbian image name
Add details about Raspbian-only NOOBS
Correct Pibrella URL
Show asterisk (it's being shown as a bullet)
Merge pull request #2 from raspberrypi/master

another update