Fix local repo paths in contributor guidance.

[deorbit]

Configuring the repository will fail with the given paths (will clone into $GOPATH/src/github.com/GoogleContainerTools, subsequent cd and git remote add will fail).

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[deorbit]

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[deorbit]

With my previous commit, import paths won't work, so I've changed guidance further to clone into $GOPATH/src/github.com/GoogleContainerTools and set the contributor's repo as a remote there after guidance by @campoy (http://blog.campoy.cat/2014/03/github-and-go-forking-pull-requests-and.html)

[nkubala]

The reason this didn't work originally is because we were missing the last part of the directory path in the git clone line:

git clone git@github.com:<your_account>/container-diff.git
$GOPATH/src/github.com/GoogleContainerTools

should be

git clone git@github.com:<your_account>/container-diff.git
$GOPATH/src/github.com/GoogleContainerTools/container-diff

That should make the flow we were trying to specify work, could you just update the original clone path?

[deorbit]

@nkubala Makes sense! I've cleaned up the branch this PR came from and issued PR #255 under a new branch of my fork.