add fcnnls example

examples/fcnnls.js

@@ -0,0 +1,14 @@
+const { fcnnlsVector } = require('../dist/ml.js').FCNNLS;
+
+// Example that allows to calculate the contribution of pure
+// spectra in a mixture.
+
+// columns correspond to pure sample
+let matrix = [[1, 1, 1], [1, 1, 0], [1, 0, 0]];
+
+let mixture = [5, 3, 1];
+
+let result = fcnnlsVector(matrix, mixture);
+console.log(result);
+
+// should be close to 1,2,2