Add option to set global no_run for doc test

[Hexilee]

As this issue.

I want to guarantee all examples in external files can pass compiling, but I would not like to run them.

The main reason not to add no_run for each block is many markdown renders cannot correctly recognize a "rust,no_run" block.

So, could we add a option for #[doc] like #[doc(include = "../README.md", no_run)]?

[jyn514]

You said "global" in the title, but your example is not global. Did you want this to be specific to included docs? Note that --no-run already exists if you want to do this for all doctests.

I'm also unsure why this is useful - why not just add no_run to the file you're including?