Document xkcd.gp usage and limitations in README

README.md

@@ -1,6 +1,25 @@
 xkcd-gnuplot
 ============
 
-How to plot xkcd-style functions with gnuplot!
+A small gnuplot example for making plots look a bit like an xkcd chart.
 
 ![Sample Graph](./xkcd.png)
+
+## Notes
+
+This is not a full xkcd rendering. The axes are still straight, and for plotted functions the random jiggle is only applied on the y coordinate. For datapoints, the same idea can be applied on both x and y.
+
+A proper solution would likely be a dedicated xkcd terminal for gnuplot, but this script keeps things simple.
+
+The script uses the Humor Sans font. The original TTF can be downloaded from antiyawn.com. For the EPS terminal, the font must be converted to PostScript PFA format. A converted `Humor-Sans.pfa` file is already included in the repository and referenced by the script.
+
+## How to use
+
+The main example is in `xkcd.gp`. Run it with gnuplot to generate `xkcd.eps`.
+
+The script defines two small helpers for adding wobble to plotted values:
+
+- `jiggle(x)` applies a small relative variation. Use it when the distortion should scale with the plotted value.
+- `jigglea(x)` applies a small absolute variation based on a fixed range. Use it when you want a fixed-size wobble.
+
+In the included example, the damped sine and cosine curves use `jiggle(...)`, while the parabola-style guide line uses `jigglea(...)`.