[README.md] added explanation about RETE algorithm added in grule

Author: newm4n

README.md

@@ -374,6 +374,35 @@ When you make your own function to be called from rule engine, you need to know
 2. The function must only return 1 type. Returning multiple variable from function are not acceptable, the rule execution will fail if there are multiple return variable.
 3. The way number literal were treated in Grule's DRL is; **decimal** will always taken as `int64` and **real** as `float64`, thus always consider to define your function argument and returns between `int64` and `float64` when your function works with numbers.
 
+## RETE Algorithm
+
+From Wikipedia : The Rete algorithm (/ˈriːtiː/ REE-tee, /ˈreɪtiː/ RAY-tee, rarely /ˈriːt/ REET, /rɛˈteɪ/ reh-TAY) is a pattern matching algorithm for implementing rule-based systems. The algorithm was developed to efficiently apply many rules or patterns to many objects, or facts, in a knowledge base. It is used to determine which of the system's rules should fire based on its data store, its facts.
+
+Some form of RETE algorithm were employed in `grule-rule-engine` starting from version `1.1.0`.
+It replaces the __Naive__ approach when evaluating rules to add to `ConflictSet`.
+ 
+`ExpressionAtom` in the DRL were compiled and will not be duplicated within the working memory of the engine.
+This makes the engine performance be increased significantly if you have many rules defined with lots of duplicated expressions
+or lots of heavy function/method calls.
+
+Grule's RETE implementation don't have `Class` selector as one expression my involve multiple class. For example an expression such as:
+
+```.go
+when
+    ClassA.attr == ClassB.attr + ClassC.AFunc()
+then
+    ...
+```
+
+The expression above involve attribute/function result comparison and math operation from 3 different class. This makes
+RETE's class separation of expression token difficult.
+
+You can read about RETE algorithm here:
+
+* https://en.wikipedia.org/wiki/Rete_algorithm
+* https://www.drdobbs.com/architecture-and-design/the-rete-matching-algorithm/184405218
+* https://www.sparklinglogic.com/rete-algorithm-demystified-part-2/ 
+
 # Tasks and Help Wanted.
 
 * Need to do more and more and more test.