cmd/tailscale: add node attribute instructions to share command help

This adds details on how to configure node attributes to allow
sharing and accessing shares.

Updates tailscale/corp#16827

Signed-off-by: Percy Wegmann <percy@tailscale.com>

cmd/tailscale/cli/share.go

@@ -140,6 +140,21 @@ func buildShareLongHelp() string {
 
 var shareLongHelpBase = `Tailscale share allows you to share directories with other machines on your tailnet.
 
+In order to share folders, your node needs to have the node attribute "tailfs:share".
+
+In order to access shares, your node needs to have the node attribute "tailfs:access".
+
+For example, to enable sharing and accessing shares for all member nodes:
+
+  "nodeAttrs": [
+    {
+      "target": ["autogroup:member"],
+      "attr": [
+        "tailfs:share",
+        "tailfs:access",
+      ],
+    }]
+
 Each share is identified by a name and points to a directory at a specific path. For example, to share the path /Users/me/Documents under the name "docs", you would run:
 
   $ tailscale share add docs /Users/me/Documents
@@ -158,6 +173,7 @@ In order to access this share, other machines on the tailnet can connect to the
 
 Permissions to access shares are controlled via ACLs. For example, to give yourself read/write access and give the group "home" read-only access to the above share, use the below ACL grants:
 
+  "grants": [
     {
       "src": ["mylogin@domain.com"],
       "dst": ["mylaptop's ip address"],
@@ -177,9 +193,11 @@ Permissions to access shares are controlled via ACLs. For example, to give yours
           "access": "ro"
         }]
       }
-	}
+    }]
 
 To categorically give yourself access to all your shares, you can use the below ACL grant:
+
+  "grants": [
     {
       "src": ["autogroup:member"],
       "dst": ["autogroup:self"],
@@ -189,8 +207,7 @@ To categorically give yourself access to all your shares, you can use the below
           "access": "rw"
         }]
       }
-	},
-
+    }]
 
 Whenever either you or anyone in the group "home" connects to the share, they connect as if they are using your local machine user. They'll be able to read the same files as your user and if they create files, those files will be owned by your user.%s