Schema: Update Text of System Fields

[zcolah]

Describe the bug
There is a grammatical error in the system fields text. See video for more context: https://www.loom.com/share/8354607ecc6c45d983991b6d783dce96

Solution
Please update the system fields text to be:
"Each content item (child) of a model in Zesty comes included with non-editable system fields that represent the state of the content such as when it was created, updated, and the version. The value of these fields can be found under the meta key in the Instances API end point."