Update documentation for ind-def:textfilecontent54_object/instance for value = 0

[solind]

Describe the bug
Remember OVALProject/Language#277?

Well, the schema documentation discusses positive and negative numbers in the context of the ind-def:textfilecontent54_object/instance entity -- but we don't talk about what to do if the value is set to 0.

Replication Steps (if applicable)
N/A

Expected behavior
We should probably clarify that we actually mean negative integers, and non-negative integers (instead of positive integers).

Content
I've seen CIS compliance content designed to look for instance "greater than" to 0. These can be safely changed to "greater than or equal" to 1, but that's just a work-around to avoid the ambiguity of the standard.

OVAL details (complete all those relevant)

• Schema: ind-def/ind-sc
• Test: textfilecontent54_test
• Object: textfilecontent54_object
• State: textfilecontent54_state
• Item: textfilecontent54_item

Additional context
More of an "oh by the way" -- the schema documentation also refers to the operation enumeration value "greater than or equal" as "greater than or equals[sic]", which is incorrect. We should fix that, too.

[wmunyan]

Closing this issue as it's already been merged into the "development" branch.