GraphQL: Add documentation for customerOrders query

[keharper]

Community engineering issue

Type of Doc:

• New topic
• Topic Update, Devdoc link:
• Other

Magento 2 GitHub Issue: magento/graphql-ce#41

Magento 2 GitHub PR: magento/graphql-ce#212

Magento 2 version:

• 2.1.X
• 2.2.X
• 2.3.X
• back port
• forward port

Notifications of Changes:

• Changes to Admin interface?
• New software requirements?
• New REST endpoints or updated GraphQL query syntax?
• New command line option?

Content

GraphQL PR-212 adds the SalesGraphQl module. Currently, the customerOrders query is the only query/mutation defined.

[keharper]

Closed per #3855