website: Just fixing a small error in the text.

The sentence was missing a few words.
I've made it read similar to the previous 3 sentences.

provisioner/shell: execute script directly instead of using /bin/sh

/cc @sgirones

/cc @sgirones

builder/virtualbox: Local mode for VBoxGuestAdditions. Provide local path and SHA256

website: Shutdown Command in Examples

website: Fix some typos and an error in the website documentation

website: Use free-tier instance size.

README: Clarify repository placement relative to GOPATH

website: Fix introduction basic example

If you don't put the repository in the right place in GOPATH,
changes to your sources don't get built.
Signed-off-by: Emil Sit <sit@emilsit.net>