Fix what is a Building Block

[avillar]

From Scott:

We need to reference the policy that established the building blocks: https://docs.ogc.org/pol/05-020r29/05-020r29.html#building-bloocks. We also need to be a little clear on definition: the “building block” is the element from the Standard, the opening sentence of the page would better read “A Building Block is a component of a specification…” and then have a second sentence that states this building block can be packaged for reuse… which is what the rest of the page describes.

CC: @rob-metalinkage @doublebyte1

[doublebyte1]

@avillar @rob-metalinkage I think that the definition of building block here is quite generic, probably to allow different sources of building blocks. However, we should not loose sight that this page is called "OGC Location Building Blocks" and thus we should add something there specifically about the building blocks of OGC Standards.

I added some information on this PR: #3