Improve hir_effect.inc.rs documentation

Author: jacob-shops

zjit/src/hir_effect/gen_hir_effect.rb

@@ -85,7 +85,15 @@ def to_graphviz effect, f
 
 # ===== Finished generating the DAG; write Rust code =====
 
-puts "// This file is @generated by src/hir/gen_hir_effect.rb."
+puts "// This file is @generated by src/hir_effect/gen_hir_effect.rb."
+puts ""
+puts "// The bits module demarcates common bit patterns we'd like to refer to by"
+puts "// name, rather than through a series of unions of labeled EffectBits."
+puts ""
+puts "// effect_types and abstract_heaps modules follow the same pattern and label"
+puts "// commonly used values."
+puts ""
+puts "// Please refer to src/hir_effect/mod.rs for further documentation."
 puts "mod bits {"
 $bits.keys.sort.map {|effect_name|
   subeffects = $bits[effect_name].join(" | ")