ISSUE-37: short description of model

For the model, we had a go at describing the essence of LDP. 

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The LDP protocol provides the mechanism to observe and evolve state through interaction with resources and their outgoing arcs. 
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regards, 
Roger

p.s. Some alternatives : 
* Linked Data is a description of observable state, and the LDP protocol provides the mechanism to evolve that state. The outgoing arcs of a resource fully define its nature; manipulation of the arcs effect the evolution thereof.
* State is composed of resources which are described using Linked Data representations. The LDP protocol provides the mechanism to evolve that state through manipulation of each resource's outgoing arcs.

p.p.s. The word 'container' wasn't necessary in the descriptions (?)