[Editorial ] invoiceIssuerName: convert normative statements in bulle…

…t points (#623)

Linked to Issue #606 that converts normative verbose statements into
bullet points.

specification/columns/invoiceissuer.md

@@ -3,7 +3,10 @@
 An Invoice Issuer is an entity responsible for invoicing for the [*resources*](#glossary:resource) or [*services*](#glossary:service) consumed. It is commonly
 used for cost analysis and reporting scenarios.
 
-The InvoiceIssuer column MUST be present in a [*FOCUS dataset*](#glossary:FOCUS-dataset). This column MUST be of type String and MUST NOT contain null values.
+The InvoiceIssuer column adheres to the following requirements:
+
+* The InvoiceIssuer column MUST be present in a [*FOCUS dataset*](#glossary:FOCUS-dataset).
+* This column MUST be of type String and MUST NOT contain null values.
 
 See [Appendix: Origination of cost data](#originationofcostdata) section for examples of [Provider](#provider), [Publisher](#publisher) and
 Invoice Issuer values that can be used for various purchasing scenarios.