Update README to use ~ for the home directory

Using ~ to specify the home directory should allow anyone to copy/paste the example. Also, this makes all the references the same. 
Previously there was a /home/sven and a /Users/sven.
Revert changes to "config" parameters

Per comment on the pull request, I've reverted the changes to the example parameters. I still believe the create config section should be changed as anyone can then copy/paste the command to create their config file without having to edit the command.
Use efficient cache in Dockerfile

It seems that this caches slightly better than `go get ./...`,
since there are only two packages.

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>
Switch to direct DNS pass-through
Merge pull request #312 from jgeiger/patch-2

Update README to use ~ for the home directory
Merge pull request #320 from tianon/direct-dns

Switch to direct DNS pass-through
Merge pull request #319 from nathanleclaire/dockerfile_cache

Use efficient cache in Dockerfile
Bump to v1.4.0
Add support for upgrading binaries

`boot2docker upgrade` will support the Docker client binary,
boot2docker-cli binary, and boot2docker ISO now.

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>
Add small doc section on upgrade

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>