Enhance Documentation for i18n Sync Script in Contributing Guidelines

[zairahira]

In my opinion, the sync-i18n part can be improved a bit.

Some more clarity can be added here:

# Current doc
So now you need to use this tool to bring the other languages in sync.

Why are these changes needed now and not before?

# Current doc
If you have changed tests or seed code of the steps in a way that is not compatible with the previous version, you first need to delete the changed files or the whole project folder for the other languages.

• Do folders and files need to be removed in all languages? In which situations is removing a folder better than removing just files?

Other suggestion

• Also, it would be worth mentioning it to the campers to expect a large number of files to be changed.

[naomi-lgbt]

We should also document the new FCC_BLOCK cli variable to allow for syncing only a specific set of challenges.