Add instructions on syncing from the snapshot

Author: gumb0

doc/index.rst

@@ -4,3 +4,4 @@ Internal documentation
 1. `Dependencies <dependencies.rst>`_
 2. `Database Layout <database_layout.rst>`_
 3. `Generating Consensus Tests <generating_tests.rst>`_
+4. `Using snapshot sync <snapshot_sync.rst>`_

doc/snapshot_sync.rst

@@ -0,0 +1,38 @@
+Using snapshot sync
+===============
+
+Snapshot sync feature is still work in progress and currently is not very user-friendly yet. These are the instructions to make it work with the main net as of December 2017.
+
+If you have Parity installed, alternative to the `Downloading snapshot` steps below is to get it from the directory like ``Parity/Ethereum/chains/ethereum/db/906a34e69aec8c0d/snapshot``
+
+Downloading the snapshot
+------
+
+1. Build cpp-ethereum from the ``snapshot-download`` branch
+::
+  git checkout snapshot-download
+  git submodule update
+  make eth
+
+2. Start downloading providing the path to the directory to save the snapshot into and the address of a running node with main net snapshot (can be a Parity node or a cpp node with imported snapshot)
+::
+  eth/eth --download-snapshot SNAPSHOT_DIR -v 9 --peerset required:493d52068ec72230688da539926f47a452b762bc348d2ab1491f399b532186d71d7c512e09ffb8e9c24d292d064c00f6234ef1221bc0d86093d2de32358d33da@52.169.85.130:30303 --pin --no-discovery
+
+The one above is cpp node, if it doesn't work try one of the Parity boot nodes from https://github.com/paritytech/parity/blob/master/ethcore/res/ethereum/foundation.json#L176
+
+3. Exit (Ctrl-C) when it says ``Snapshot download complete!``
+
+Importing the snapshot
+------
+
+1. Build cpp-ethereum from the latest ``develop`` branch
+::
+  git checkout develop
+  git submodule update
+  make eth
+
+2. Start importing the snapshot providing the path to the snapshot directory
+::
+  eth/eth --import-snapshot SNAPSHOT_DIR -v 8
+
+3. After import is complete, it will automatically switch to regular sync process to get the blocks between snapshot and the current chain head.