Update semantics.md to improve readability of example

[rat10]

In my experience an example is more readable if additional detail is introduced after the main fact. In this example the property :b is part of the main fact and the owl:sameAs relation between :b and :c is the additional detail. First seeing :b used and then being informed about the relation of :b to something else makes the example more readable IMHO.

[pfps]

I set up the order so that the 'background' (equality) information comes first, which I find more natural.

[rat10]

I understand, and I concur that this might be a highly subjective matter. However, to me the cognitive load seems much higher when I first have to ingest information without knowing the purpose. The purpose of the sameAs statement only becomes clear when :b is actually put to good use in the second statement. Therefore I prefer to read the core of the example first and then get introduced to the additional detail (of the sameAs relation). With this I rest my case :)