Add more descriptive image to docs - especially Design section.

[nerodk89]

We need to add more descriptive images to the Walrus docs, especially in the Design -> Architecture section.
To show the connection between Blob, Slivers, Shards, Storage Nodes.

[nerodk89]

Something just like this one

[mlegner]

Thank you for the suggestion. I've been wanting to do this for a while but never found the time. I now created a separate issue for this: #109.

[nerodk89]

Ok, let me contribute some pics to this. I'm researching Walrus, so I also need to verify my knowledge. Thanks.