RTC 4.0.1 Requirement CR
Accepted answer
I'm not an expert on this, but I believe this is used to support external RM tools that want to use RTC to mange change requests to requirements (as opposed to CRs for software). This option maps the OSLC-defined alias "Requirement CR" to an RTC work item type.
So an external product (like DOORS) can use RTC to manage change request to requirements. The selected RTC WI type is what's used to mange those requirement CRs.
You can see an example of how to use RTC to manage requirement CRs in DOORS here: https://jazz.net/library/LearnItem.jsp?href=content/articles/rtc/3.0/configuring-doors-and-rtc-to-integrate/index.html
One other answer
I found this in the mapping section of the 4.0.2 Information center:
In the Requirement CR row, select the work item type to map to a requirement change request.
In the Requirement CR row, select the work item type to map to a requirement change request.