Clarify the meaning of multi-part OSLC Core 3.0 specification re: conformance

I added this paragraph at the end of section 5. OSLC Core 3.0: These documents comprise the multi-part specification for OSLC Core 3.0. They represent common capabilities that servers MAY provide and that may be discovered and used by clients. Although OSLC Core could be useful on its own, it is intended to specify capabilities that are common across many domains. Servers will generally specify conformance with specific domain specifications, and those domain specifications will describe what parts of OSLC Core are required for conformance. This allows servers to implement the capabilities they need in a standard way without the burden of implementing capabilities that are not required. The purpose of OSLC Core Discovery capability is to allow clients to determine what capabilities are provided by a server. Any provided capability must meet all the conformance criteria for that capability as defined in the OSLC Core 3.0 specifications. This implies that any capability that is discoverable is essentially optional, and once discovered, the capability is provided as defined in the applicable OSLC specifications. Servers should support OSLC Discovery, but Discovery itself is also an optional capability as servers could provide other means of informing specific clients of supported OSLC capabilities that could be utilized directly. For example, a server might provide only preview dialogs on specific resources and nothing else.