Document the auto-label style setting

SourceGen/RuntimeData/Help/settings.html

@@ -201,6 +201,12 @@ declare it a string.  Shorter values are prone to false-positive
 identifications, longer values miss out on short strings.  You can also
 set it to "none" to disable automatic string identification.</p>
 
+<p>The auto-label style setting determines the format for labels that are
+generated automatically.  By default the label will be the letter 'L'
+followed by the hexadecimal address, but the label can be annotated based
+on usage.  For example, addresses that are the target of branch instructions
+can be labeled with the letter 'B'.</p>
+
 
 <h3><a name="projprop-projsym">Project Symbols</a></h3>
 <p>You can add, edit, and delete individual symbols and constants.

SourceGen/XrefSet.cs

@@ -35,6 +35,8 @@ namespace SourceGen {
             BranchOp,           // branch instruction
             RefFromData,        // reference in data area, e.g. ".dd2 <address>"
             MemAccessOp,        // instruction that accesses memory, or refers to an address
+            // TODO(someday): track 16-bit vs. 24-bit addressing, so we can show whether
+            //   something is a "far" reference (and maybe carry this into auto-label annotation)
         }
 
         /// <summary>