docs: organize the directory, #656

docs/specification/light-client-protocol.rst

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+Light Client Protocol
+=====================
+
+Light clients are an important part of the complete blockchain system
+for most applications. Tendermint provides unique speed and security
+properties for light client applications.
+
+See our developing `light-client
+repository <https://github.com/tendermint/light-client>`__.
+
+Overview
+--------
+
+The objective of the light client protocol is to get a
+`commit <./validators.html#committing-a-block>`__ for a recent
+`block hash <./block-structure.html#block-hash>`__ where the commit
+includes a majority of signatures from the last known validator set.
+From there, all the application state is verifiable with `merkle
+proofs <./merkle.html#iavl-tree>`__.
+
+Properties
+----------
+
+-  You get the full collateralized security benefits of Tendermint; No
+   need to wait for confirmations.
+-  You get the full speed benefits of Tendermint; transactions commit
+   instantly.
+-  You can get the most recent version of the application state
+   non-interactively (without committing anything to the blockchain).
+   For example, this means that you can get the most recent value of a
+   name from the name-registry without worrying about fork censorship
+   attacks, without posting a commit and waiting for confirmations. It's
+   fast, secure, and free!