Add README file to lifting project

lifting/README.md

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+lifting
+=======
+
+This package contains the source code for the paper **The (not so) Trivial
+Lifting in Two Dimensions**, by Ricardo Fukasawa, Laurent Poirrier and Álinson
+S. Xavier.
+
+Required Tools and Libraries
+----------------------------
+
+To produce the tables in the paper, the following tools and libraries were
+used. Different versions may produce slightly different outputs.
+
+- GNU Make, version 3.81
+- CMake, version 3.5.1
+- GCC, the GNU Compiler Collection, version 4.8.4
+- Ruby, version 1.9.3
+- IBM® ILOG® CPLEX®, version 12.6
+
+Build instructions
+------------------
+
+1. Navigate to the folder `../build`
+2. Run `cmake ..` followed by `make lifting-benchmark.run`
+3. Two binaries (`lifting-benchmark.run` and `liblifting.a`) will be generated
+
+Running the experiments
+-----------------------
+
+1. Build the project, following the instructions above.
+2. Navigate to the folder `lifting/benchmark` and execute
+
+        ./run_experiments.sh
+
+3. Two CSV files will be generated inside the folder `lifting/benchmark/tables`,
+	corresponding to the two tables that appear in the paper.
+
+In order to run the experiments with a different set of instances,
+the file `lifting/benchmark/instances/filtered/all.txt` should be modified.
+Each line in this file describes the origin `f` and a lattice-free set `B`.
+The set `B` is described by the coordinates of its vertices. Since the generator
+only deals with maximal lattice-free sets, it is also necessary to specify the
+lattice-point in the relative interior of each facet of `B`. The format of the file
+is as follows:
+
+	f[0] f[1] n v[0][0] v[0][1] ... v[n-1][0] v[n-1][1] n l[0][0] l[0][1] ... l[n-1][0] l[n-1][1]
+
+where `n` is the number of facets, `v` is a n-by-2 matrix of doubles
+corresponding to the vertices and l is an n-by-2 matrix of doubles
+corresponding to the lattice-points.