If no code block can be found, throw an error

[christian-bromann]

Current Behavior

If the markdown file has no code block, runme just prints:

runme ls
NAME  FIRST COMMAND  # OF COMMANDS  DESCRIPTION

Desired Behavior

I suggest to be more explicit and throw an error, e.g. No code block found in "Readme.md", get started writing code blocks here: ....`

[adambabik]

It makes sense. The error printed into stderr + non-zero return code.