docs: add bootstrap proto documentation

bootstrap/service.proto

@@ -7,14 +7,19 @@ import "github.com/gogo/protobuf/gogoproto/gogo.proto";
 
 option (gogoproto.stable_marshaler_all) = true;
 
-// The Bootstrap service definition.
+// Bootstrap service allows neofs-node to connect to the network. Node should
+// perform at least one bootstrap request in the epoch to stay in the network
+// for the next epoch.
 service Bootstrap {
+    // Process is method that allows to register node in the network and receive actual netmap
     rpc Process(Request) returns (bootstrap.SpreadMap);
 }
 
-// Request message to communicate between DHT nodes
 message Request {
+    // Type is NodeType, can be InnerRingNode (type=1) or StorageNode (type=2)
     int32              type = 1 [(gogoproto.customname) = "Type" , (gogoproto.nullable) = false, (gogoproto.customtype) = "NodeType"];
+    // Info contains information about node
     bootstrap.NodeInfo info = 2 [(gogoproto.nullable) = false];
+    // TTL must be larger than zero, it decreased in every neofs-node
     uint32 TTL           = 3;
 }

bootstrap/types.proto

@@ -10,13 +10,19 @@ option (gogoproto.stringer_all) =  false;
 option (gogoproto.goproto_stringer_all) = false;
 
 message SpreadMap {
+    // Epoch is current epoch for netmap
     uint64 Epoch = 1;
+    // NetMap is a set of NodeInfos
     repeated NodeInfo NetMap = 2 [(gogoproto.nullable) = false];
 }
 
 message NodeInfo {
+    // Address is a node [multi-address](https://github.com/multiformats/multiaddr)
     string Address          = 1 [(gogoproto.jsontag) = "address"];
+    // PubKey is a compressed public key representation in bytes
     bytes PubKey            = 2 [(gogoproto.jsontag) = "pubkey,omitempty"];
+    // Options is set of node optional information, such as storage capacity, node location, price and etc
     repeated string Options = 3 [(gogoproto.jsontag) = "options,omitempty"];
+    // Status is bitmap status of the node
     uint64 Status           = 4 [(gogoproto.jsontag) = "status", (gogoproto.nullable) = false, (gogoproto.customtype) = "NodeStatus"];
 }