Onboarding if no README present

[mxsdev]

Currently, we just throw an error if a README file isn't present. This is a good opportunity to do some onboarding for making a new readme file.

Maybe also we can introduce a runme init command to auto-generate a runme-friendly README file?

[christian-bromann]

@sourishkrout I think we can close this, Runme now suggest cells to run based on other markdown files in the project:

❯ ls -la
total 8
drwxr-xr-x   3 christianbromann  wheel    96 Aug 11 15:00 .
drwxrwxrwt  34 root              wheel  1088 Aug 11 14:58 ..
-rw-r--r--   1 christianbromann  wheel    54 Aug 11 15:00 CONTRIBUTING.md
❯ runme
runme 1.6.0

> echo-hello (unnamed) CONTRIBUTING.md
    echo "Hello World!"


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That said, there is a case where it throws an error when no markdown file is found in the project. Should we in this case suggest to create a README.md with some example content?