Add install_instructions to _includes directory.

[vinisalazar]

Hi,

The workshop-template repository has an install_instructions/ folder in the _includes directory that is rather handy, as it allows to include HTML blocks in the setup.md file. I am working on a couple of lessons that use the remote theme and would like to use these HTML blocks to provide installation instructions, but currently I have to create an _includes directory just to store the desired HTML file, as they are not available from this remote theme. Adding these files to the remote theme would make it easier to integrate these files, sparing the need to create an _includes directory only for them.

Summary of changes:

• Creates install_instructions folder inside the _includes directory, copied from the workshop-template repository.

Thank you for any assistance you can provide,
Vini