Document example of how to format the --headers parameter in the i18n make-pot command

[helgatheviking]

The docu says it's a JSON-formatted array, but I've been fighting to get it to run via composer and can't see to figure it out. An example might be nice.... especially for the "Report-Msgid-Bugs-To" header.

[swissspidy]

wp i18n make-pot wp-content/plugins/hello-world wp-content/plugins/hello-world/languages/hello-world.pot --headers='{"Report-Msgid-Bugs-To":"https://github.com/hello-world/hello-world/"}'

If you'd like to submit a PR with some examples that you think would be useful for others, we appreciate all contributions :)