Add papers presented on SF chapter on Feb 23rd 2017 (#432)

- NOTE: The paper "A Unified Theory of Garbage Collection" was already
  present in the garbage collection section, so I just added a brief
  summary.

data_replication/README.md

@@ -1,4 +1,8 @@
 # Data Replication
 
-* :scroll: [A comprehensive study of
Convergent and Commutative Replicated Data Types](a-comprehensive-study-of-convergent-and-communative-replicated-data-types.pdf)
+* :scroll: [Immutability Changes Everything](http://cidrdb.org/cidr2015/Papers/CIDR15_Paper16.pdf)
+    > An overview on the patterns in computing leveraging immutability. 
+    Nowadays, keeping immutable copies of data is almost inexpensive. One of the advantages of this fact is that it 
+    can alleviate the burden of coordinated accesses to the data in the different layers of the SW/HW stack.
+* :scroll: [A comprehensive study of Convergent and Commutative Replicated Data Types](a-comprehensive-study-of-convergent-and-communative-replicated-data-types.pdf)
     > Eventual consistency aims to ensure that replicas of some mutable shared object converge without foreground synchronisation.  We study a principled approach: to base the design of shared data types on some simple formal conditions that are sufficient to guarantee even- tual consistency. We call these types Convergent or Commutative Replicated Data Types (CRDTs).

garbage_collection/README.md

@@ -1,4 +1,5 @@
 * [A Unified Theory of Garbage Collection](http://www.cs.virginia.edu/~cs415/reading/bacon-garbage.pdf)
+    > An overview for programmers and language implementors for understanding different garbage collection algorithms.
 * [A LISP Garbage-Collector for Virtual-Memory Computer Systems](https://www.cs.purdue.edu/homes/hosking/690M/p611-fenichel.pdf)
 
 * [Incremental Collection of Mature Objects](http://pdf.aminer.org/000/465/194/incremental_collection_of_mature_objects.pdf)