GISAS reference

hugo/content/py/sim/gisas/_index.md

@@ -5,8 +5,29 @@ weight = 30
 
 ## GISAS simulation
 
-In BornAgain, grazing-incidence small-angle scattering (GISAS)
-is computed using the distorted-wave Born approximation (DWBA).
+To set up and run a scattering simulation, use
+```python
+import bornagain as ba
+beam = ...
+sample = ...
+detector = ...
+simulation = ba.ScatteringSimulation(scan, sample, detector)
+# ... set options
+result = simulation.simulate()
+```
+
+For the constructor arguments, see sections [beam]({{% ref-py "instr/beam" %}}),
+[sample]({{% ref-py "sample" %}}), and [detector]({{% ref-py "instr/det" %}}).
+
+For optional settings, see [simulation options]({{% ref-py "sim/options" %}}).
+Furthermore, there are examples
+for [setting masks]({{% ref-py "fitting/advanced/fit-with-masks" %}})
+and [setting a region of interest]({{% ref-py "fitting/instrument-description" %}}).
+
+For the return type of function `simulate()`,
+see [SimulationResult]({{% ref-py "result/simulation-result" %}}).
+
+### Example
 
 In the following introductory example,
 we take a standard sample model from module
@@ -39,7 +60,7 @@ The spherical detector has nPix=200 bins for both coordinate axis.
 The azimuthal angle $\varphi\_\text{f}$ extends from $-2^\circ$ to $+2^\circ$;
 the glancing angle $\alpha\_\text{f}$ from $0^\circ$ to $3^\circ$.
 
-### Main program
+#### Main program
 
 The last stance in the script is the main program.