camera: Add libopencv-dev package to installation instructions

Author: naushir

documentation/asciidoc/computers/camera/rpicam_apps_building.adoc

@@ -27,7 +27,7 @@ To build `rpicam-apps` without first rebuilding `libcamera` and `libepoxy`, inst
 
 [source,console]
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-$ sudo apt install -y libcamera-dev libepoxy-dev libjpeg-dev libtiff5-dev libpng-dev
+$ sudo apt install -y libcamera-dev libepoxy-dev libjpeg-dev libtiff5-dev libpng-dev libopencv-dev
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 TIP: If you do not need support for the GLES/EGL preview window, omit `libepoxy-dev`.