Increase default memory size to 2G

This avoids running out of /tmp space during the integration tests
which run as part of Docker's `make test`.

See https://github.com/dotcloud/docker/issues/6331.
Update docs for 2G memory default

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)
Fix sed command to find VM IP address in readme

The `-E` flag is needed to make `+` work in the version of sed in
OS X.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Merge pull request #156 from bfirsh/fix-command-to-find-vm-ip-in-readme

Fix sed command to find VM IP address in readme
Merge pull request #151 from glyn/master

Increase default memory size to 2G
point out that there is now a boot2docker ip command