Improve installation instructions

Add note about needing libvips dependencies in production, as well as
development.

docs/users/installation.md

@@ -25,7 +25,8 @@ sort: 1
 3. Install `libvips`. Most package managers know about it, otherwise it can be found
    [here](https://libvips.github.io/libvips/install.html).
 4. Install libvips dependencies for all image formats you will use, such as `libpng`, `libwebp`,
-   `libjpeg`, and `libheif` (for avif).
+   `libjpeg`, and `libheif` (for avif). Note that if you use a deployment or CI service, these
+   dependencies will be required there as well.
 5. Optional: Install `ImageMagick` for additional image formats. If vips runs into an image format
    it can't handle (jp2 on my particular installation), JPT will instruct it to try ImageMagick
    instead.