Explain that .bundle should be added to linked_dirs

[mattbrictson]

As explained in #95, the bundle check behavior used by this gem depends on .bundle/config from previous deployments. If this directory is not linked, bundle check will be ineffective and a slower bundle install will be used. This unnecessarily slows down deployments.

We should add this explanation to the README.

[mattbrictson]

Closed via #102

[allaire]

@mattbrictson Quick question, I don't have .bundle in my linked_dirs. I'm using capistrano-rails and it's not in the README (but vendor/bundle is). AFAIK, bundle check is still working correctly, even though .bundle is not linked, is it because vendor/bundle is? Should I also add .bundle to be safe?

Let me know and I will update the README of capistrano-rails if that's the case!

[mattbrictson]

@allaire Yes, I agree this should also be added to the capistrano-rails README. If you'd be willing to open a PR, that would be much appreciated!

As discussed in #95, bundle check doesn't accept the --without option, so unless .bundle/config is already present, it will check whether all of the Gemfile dependencies are satisfied, not just the production ones. So I am pretty sure linking .bundle it is necessary for check to work as intended.

[allaire]

@mattbrictson Great, gonna add it quick to the README :)