Ruby: Add missing QL doc

Author: hvitved

ruby/ql/lib/codeql/ruby/ast/Scope.qll

@@ -3,12 +3,20 @@ private import internal.AST
 private import internal.Scope
 private import internal.TreeSitter
 
+/**
+ * A variable scope. This is either a top-level (file), a module, a class,
+ * or a callable.
+ */
 class Scope extends AstNode, TScopeType instanceof ScopeImpl {
+  /** Gets the outer scope, if any. */
   Scope getOuterScope() { result = super.getOuterScopeImpl() }
 
+  /** Gets a variable declared in this scope. */
   Variable getAVariable() { result = super.getAVariableImpl() }
 
+  /** Gets the variable named `name` declared in this scope. */
   Variable getVariable(string name) { result = super.getVariableImpl(name) }
 }
 
+/** A scope in which a `self` variable exists. */
 class SelfScope extends Scope, TSelfScopeType { }