adds README section regarding usage in child procs

[kristofkalocsai]

code example and original request copied from @aaarichter
should close #811

[Qix-]

Thanks for opening this PR, just a small change.

[kristofkalocsai]

could you please add the label hacktoberfest-accepted if you merge the PR?

[Qix-]

I would really rather not as it attracts really spammy contributions, thus I tend not to 'participate' in Hacktoberfest. However I've tweeted at them to see if there's a way to still give you credit somehow without opening up this repo to an onslaught of spam.

Let's see what they say :)

[kristofkalocsai]

Understandable :D
Thanks for going the extra mile, appreciated!

[Qix-]

Hey I've not received a response but I'd still like to merge this. Are you okay if this doesn't get recognized by Hacktoberfest? Sorry about that.

Feel free to reach out to them and comment back here with something I can do either now or post-merge to singularly mark this as having participated.

[kristofkalocsai]

Of course, go ahead, thanks!

[Qix-]

Thank you so much :) Very appreciated.