[#275] netmap: Re-format the package docs

Start package docs with commonly used format `Package netmap ...`. Also
make `gofmt` do the job.

Signed-off-by: Leonard Lyubich <[email protected]>

netmap/doc.go

@@ -1,34 +1,34 @@
 /*
-Netmap contract is a contract deployed in NeoFS sidechain.
+Package netmap contains implementation of the Netmap contract for NeoFS systems.
 
 Netmap contract stores and manages NeoFS network map, Storage node candidates
 and epoch number counter. In notary disabled environment, contract also stores
 a list of Inner Ring node keys.
 
-Contract notifications
+# Contract notifications
 
 AddPeer notification. This notification is produced when a Storage node sends
 a bootstrap request by invoking AddPeer method.
 
-  AddPeer
-    - name: nodeInfo
-      type: ByteArray
+	AddPeer
+	  - name: nodeInfo
+	    type: ByteArray
 
 UpdateState notification. This notification is produced when a Storage node wants
 to change its state (go offline) by invoking UpdateState method. Supported
 states: (2) -- offline.
 
-  UpdateState
-    - name: state
-      type: Integer
-    - name: publicKey
-      type: PublicKey
+	UpdateState
+	  - name: state
+	    type: Integer
+	  - name: publicKey
+	    type: PublicKey
 
 NewEpoch notification. This notification is produced when a new epoch is applied
 in the network by invoking NewEpoch method.
 
-  NewEpoch
-    - name: epoch
-      type: Integer
+	NewEpoch
+	  - name: epoch
+	    type: Integer
 */
 package netmap