fix: readme and static const DT

advection/README.md

@@ -1,3 +1,28 @@
+## What is new?
+There is one new added component: `AdvectionKernel`s which is an "interface" (i.e an abstract class).
+There are two implementations simple Euler integration called `EulerIntegrationKernel` and 
+Runge Kutta integration called `RK4AdvectionKernel`.
+
+Main function gives a good example of how to use the library. Especially the following function which prints the
+position of the particle at every time step.
+```Cpp
+template <typename AdvectionKernelImpl>
+void advectForSomeTime(const UVGrid &uvGrid, const AdvectionKernelImpl &kernel, double latstart, double lonstart) {
+
+    // Require at compile time that kernel derives from the abstract class AdvectionKernel
+    static_assert(std::is_base_of<AdvectionKernel, AdvectionKernelImpl>::value, NotAKernelError);
+
+    double lat1 = latstart, lon1 = lonstart;
+    for(int time = 100; time <= 10000; time += AdvectionKernel::DT) {
+        cout << "lat = " << lat1 << " lon = " << lon1 << endl;
+        auto [templat, templon] = kernel.advect(time, lat1, lon1);
+        lat1 = templat;
+        lon1 = templon;
+    }
+}
+```
+
+
 ## Location of data
 The data path is hardcoded such that the following tree structure is assumed:
 ```