Merge pull request #538 from mattcode55/536-fluffyblocks

Create Fluffy Blocks Moneropedia entry

resources/moneropedia/fluffyblocks.md

+---
+layout: moneropedia
+entry: "Fluffy Blocks"
+terms: ["fluffy blocks", "fluffyblocks"]
+summary: "a way of saving bandwidth when sending new blocks around the network"
+---
+
+### The Basics
+
+A @block is made up of a header and @transactions. Fluffy Blocks only contain
+a header, a list of transaction indices, and any transactions that the node
+recieving the block may be missing. This saves bandwidth because nodes might
+already know about most or all of the transactions in the block and they don't
+need to be sent them again.
+
+### See Also
+
+* [BIP152 "Compact Block Relay"](https://github.com/bitcoin/bips/blob/master/bip-0152.mediawiki)
+* [Xthin](https://github.com/BitcoinUnlimited/BitcoinUnlimited/blob/release/doc/bu-xthin-protocol.md)