[Doc] Add initializer description

lib/cocoapods/installer/analyzer/pod_variant.rb

@@ -22,6 +22,8 @@ module Pod
           specs.first.root
         end
 
+        # Initialize a new instance from its attributes.
+        #
         # @param [Array<String>] specs       @see #specs
         # @param [Platform] platform         @see #platform
         # @param [Bool] requires_frameworks  @see #requires_frameworks?

lib/cocoapods/installer/analyzer/pod_variant_set.rb

@@ -7,6 +7,8 @@ module Pod
         #
         attr_accessor :variants
 
+        # Initialize a new instance.
+        #
         # @param [Array<PodVariant>] variants  @see #variants
         #
         def initialize(variants)