Deprecate/refactor content in docs/specification (#1934)

* docs: deprecate specification dir, closes #1814

* update genesis

* old spec dir, deprecation complete

* rm a file

docs/tendermint-core/using-tendermint.md

@@ -31,6 +31,73 @@ For more elaborate initialization, see the tesnet command:
 tendermint testnet --help
 ```
 
+### Genesis
+
+The `genesis.json` file in `$TMHOME/config/` defines the initial
+TendermintCore state upon genesis of the blockchain ([see
+definition](https://github.com/tendermint/tendermint/blob/master/types/genesis.go)).
+
+#### Fields
+
+-   `genesis_time`: Official time of blockchain start.
+-   `chain_id`: ID of the blockchain. This must be unique for
+    every blockchain. If your testnet blockchains do not have unique
+    chain IDs, you will have a bad time.
+-   `validators`:
+-   `pub_key`: The first element specifies the `pub_key` type. 1
+    == Ed25519. The second element are the pubkey bytes.
+-   `power`: The validator's voting power.
+-   `name`: Name of the validator (optional).
+-   `app_hash`: The expected application hash (as returned by the
+    `ResponseInfo` ABCI message) upon genesis. If the app's hash does
+    not match, Tendermint will panic.
+-   `app_state`: The application state (e.g. initial distribution
+    of tokens).
+
+#### Sample genesis.json
+
+```
+{
+  "genesis_time": "2018-07-09T22:43:06.255718641Z",
+  "chain_id": "chain-IAkWsK",
+  "validators": [
+    {
+      "pub_key": {
+        "type": "tendermint/PubKeyEd25519",
+        "value": "oX8HhKsErMluxI0QWNSR8djQMSupDvHdAYrHwP7n73k="
+      },
+      "power": "1",
+      "name": "node0"
+    },
+    {
+      "pub_key": {
+        "type": "tendermint/PubKeyEd25519",
+        "value": "UZNSJA9zmeFQj36Rs296lY+WFQ4Rt6s7snPpuKypl5I="
+      },
+      "power": "1",
+      "name": "node1"
+    },
+    {
+      "pub_key": {
+        "type": "tendermint/PubKeyEd25519",
+        "value": "i9GrM6/MHB4zjCelMZBUYHNXYIzl4n0RkDCVmmLhS/o="
+      },
+      "power": "1",
+      "name": "node2"
+    },
+    {
+      "pub_key": {
+        "type": "tendermint/PubKeyEd25519",
+        "value": "0qq7954l87trEqbQV9c7d1gurnjTGMxreXc848ZZ5aw="
+      },
+      "power": "1",
+      "name": "node3"
+    }
+  ],
+  "app_hash": ""
+}
+```
+
 ## Run
 
 To run a Tendermint node, use