[#170] acl: Document package functionality

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

acl/doc.go

@@ -0,0 +1,40 @@
+/*
+Package acl provides primitives to perform handling basic ACL management in NeoFS.
+
+BasicACL type provides functionality for managing container basic access-control list.
+For example, setting public basic ACL that could not be extended with any eACL rules:
+
+	import "github.com/nspcc-dev/neofs-sdk-go/container"
+	...
+		c := container.New()
+		c.SetBasicACL(acl.PublicBasicRule)
+
+Using package types in an application is recommended to potentially work with
+different protocol versions with which these types are compatible.
+
+	Basic ACL bits meaning:
+
+	┌──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┐
+	│31│30│29│28│27│26│25│24│23│22│21│20│19│18│17│16│ <- Bit
+	├──┼──┼──┼──┼──┴──┴──┴──┼──┴──┴──┴──┼──┴──┴──┴──┤
+	│  │  │  │  │ RANGEHASH │   RANGE   │   SEARCH  │ <- Object service method
+	│  │  │  │  ├──┬──┬──┬──┼──┬──┬──┬──┼──┬──┬──┬──┤
+	│  │  │ X│ F│ U│ S│ O│ B│ U│ S│ O│ B│ U│ S│ O│ B│ <- Rule
+	├──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┼──┤
+	│15│14│13│12│11│10│09│08│07│06│05│04│03│02│01│00│ <- Bit
+	├──┴──┴──┴──┼──┴──┴──┴──┼──┴──┴──┴──┼──┴──┴──┴──┤
+	│   DELETE  │    PUT    │   HEAD    │    GET    │ <- Object service method
+	├──┬──┬──┬──┼──┬──┬──┬──┼──┬──┬──┬──┼──┬──┬──┬──┤
+	│ U│ S│ O│ B│ U│ S│ O│ B│ U│ S│ O│ B│ U│ S│ O│ B│ <- Rule
+	└──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
+
+	U - Allows access to the owner of the container.
+	S - Allows access to Inner Ring and container nodes in the current version of network map.
+	O - Clients that do not match any of the categories above.
+	B - Allows using Bear Token ACL rules to replace eACL rules.
+	F - Flag denying Extended ACL. If set Extended ACL is ignored.
+	X - Flag denying different owners of the request and the object.
+
+	Remaining bits are reserved and are not used.
+*/
+package acl

acl/types.go

@@ -9,6 +9,8 @@ import (
 // BasicACL is Access Control List that defines who can interact with containers and what exactly they can do.
 type BasicACL uint32
 
+// String returns BasicACL string representation
+// in hexadecimal form with 0x prefix.
 func (a BasicACL) String() string {
 	return fmt.Sprintf("0x%08x", uint32(a))
 }