Add tachyon limitations

docs/dynamic-images.md

@@ -71,3 +71,12 @@ The following query string arguments can be applied to any image delivered by Ta
 |`webp`|Boolean, 1|Force WebP format.|
 |`lb`|String, "w,h"|Add letterboxing effect to images, by scaling them to width, height while maintaining the aspect ratio and filling the rest with black or `background`.|
 |`background`|String|Add background color via name (red) or hex value (%23ff0000). Don't forget to escape # as `%23`.|
+
+## Limitations
+
+Image files that contain dimensions as part of the file name, e.g.
+`my-image-100x200.png` can cause issues for Tachyon. We recommend you rename all
+images to remove dimensions from their file names, as well as any other special
+characters. You can
+use [this tool](https://github.com/humanmade/rename-images-command) as a
+framework to convert file names.