tutorials: confusing code sample and note about .dvc/cache dir

[anferico]

I was following the tutorial at https://dvc.org/doc/tutorials/deep/preparation to start exploring DVC's functionalities. However, when I issue the command dvc init inside the classify/ directory, I don't get the expected results.
In fact, ls -a .dvc should output the following:
./ ../ .gitignore cache/ config
whereas my output is:
./ ../ config .gitignore tmp/
so basically the cache/ directory doesn't get created, but a tmp/ directory does. This wouldn't be a big deal if the tutorial didn't mention that "The .dvc/cache directory is one of the most important parts of any DVC repositories"

[shcheklein]

@anferico yep, good point .. I think that we switched to creating it on-demand when we actually do some operations with it. @efiop could you confirm?

But the point stays - it's an important part. When you start doing dvc add, dvc run, etc ... you should see the directory.

[jorgeorpinel]

We should def. update the code sample and note though, so it's not confusing. This may affect other docs too. (I think that note is repeated in several places.)

[efiop]

@shcheklein I confirm :)

[jorgeorpinel]

@anferico do you think this version is less confusing? https://dvc-org-pr-810.herokuapp.com/doc/tutorials/deep/preparation

Note that the paragraph starting with "After DVC initialization..." I haven't updated yet because it's repeated in 4 different documents, but I will.

[jorgeorpinel]

@anferico please check my PR #810 if you can. That should solve this confusion. Thanks again for reporting!