Added compilation instructions and updated API ref

README.md

@@ -5,10 +5,28 @@ A C++ ensemble of functions to compute the Wigner 3j- and 6j- symbols. It implem
 by Schulten and Gordon. It can either compute an array of Wigner 3j or 6j symbols, or a single
 coefficient. It also computes the Clebsch-Gordan coefficients.
 
+## Compilation Instructions
+This library uses CMake to help the build process. First, download the source code. 
+It is recommended to create a separate directory for building, i.e.
+```bash 
+ mkdir build/.
+```
+Then, run
+```bash
+ cmake .. && make && sudo make install.
+```
+By default, the library is installed to `/usr/lib/` and the include files are in `/usr/include/`.
+To install to another directory, say `/usr/local/`, use the command-line argument
+```bash
+ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr/local && make && sudo make install.
+```
+
 ## API documentation
 We list the user-facing functions that compute the Wigner symbols. The functions are
 behind the namespace `WignerSymbols`.
 
+### C++ implementation
+
  + `std::vector<double> wigner3j(double l2, double l3, double m1, double m2, double m3)`<br />
  Computes Wigner 3j symbols with all possible values of `l1`. Returns an `std::vector<double>` with the 
  coefficients sorted by increasing values of `l1`.
@@ -22,6 +40,14 @@ behind the namespace `WignerSymbols`.
  + `double wigner6j(double l1, double l2, double l3, double l4, double l5, double l6)`<br />
  Computes a specific Wigner 6j symbol.
 
+### Fortran implementation
+
+ + `double wigner3j_f(double l1, double l2, double l3, double m1, double m2, double m3)`<br />
+ Computes a specific Wigner 3j symbol. 
+ + `double clebschGordan_f(double l1, double l2, double l3, double m1, double m2, double m3)`<br />
+ Computes a specific Clebch-Gordan coeffcient.
+ + `double wigner6j_f(double l1, double l2, double l3, double l4, double l5, double l6)`<br />
+ Computes a specific Wigner 6j symbol.
 
 ## Bibliography 
  + K. Schulten and R. G. Gordon, _Recursive evaluation of 3j and 6j coefficients_, Comput. Phys. Commun. **11**, 269–278 (1976).