Fixed typo in README.md

Author: PaulMatlashewski

README.md

@@ -174,7 +174,7 @@ interp_linear(1.05) # approximately log(1.05)
 
 ### BSplines
 
-The interpolation type is described in terms of *degree* and, if necessary, *boundary conditions*. There are currently three degrees available: `Constant`, `Linear`, `Quadratic`,  and `Cubic` corresponding to B-splines of degree 0, 1, 2, and 3 respectively.
+The interpolation type is described in terms of *degree* and, if necessary, *boundary conditions*. There are currently four degrees available: `Constant`, `Linear`, `Quadratic`,  and `Cubic` corresponding to B-splines of degree 0, 1, 2, and 3 respectively.
 
 B-splines of quadratic or higher degree require solving an equation system to obtain the interpolation coefficients, and for that you must specify a *boundary condition* that is applied to close the system. The following boundary conditions are implemented: `Flat`, `Line` (alternatively, `Natural`), `Free`, `Periodic` and `Reflect`; their mathematical implications are described in detail in the pdf document under `/doc/latex`.
 When specifying these boundary conditions you also have to specify whether they apply at the edge grid point (`OnGrid()`)