Added code examples for External Accounts API

[aloks98]

Added various cURL examples for External accounts API

[aloks98]

@lukeocodes Can you review the changes please? :)

[lukeocodes]

It looks good to me but I don't have time to test it all. I'll add Tony as a reviewer, but add hacktoberfest-accepted in the meantime.

Thank you so much your for contributions <3

[aloks98]

Sure! Let me know if any changes need :D

[tbedford]

@aloks98 Thanks for your contribution. I will get to at some point but I will need to create the specs for these first. I assume you have tested? (I will also have to set things up and test).

In the mean time a couple of suggestions:

• Would possibly be better in a top directory of external-accounts - for example: external-accounts/link-application-to-account.sh, as not really related to Accounts (more Messages API).
• Rename account/external-accounts-api/messenger/delete-a-messenger-accoun.sh to external-accounts/delete-a-messenger-account.sh (notice adds missing t on end of accoun).