note PDFium build in README

README.md

@@ -162,8 +162,31 @@ via imagemagick instead.
 
 ### PDFium
 
-If present, libvips will attempt to load PDFs via PDFium. This library must be
-packaged by https://github.com/jcupitt/docker-builds/tree/master/pdfium
+If present, libvips will attempt to load PDFs with PDFium. Download the 
+prebuilt pdfium binary from: 
+
+    https://github.com/bblanchon/pdfium-binaries
+
+Untar to the libvips install prefix, for example:
+
+    cd ~/vips
+    tar xf ~/pdfium-linux.tgz
+
+Create a `pdfium.pc` like this (update the version number):
+
+    VIPSHOME=/home/john/vips
+    cat > $VIPSHOME/lib/pkgconfig/pdfium.pc << EOF
+         prefix=$VIPSHOME
+         exec_prefix=\${prefix}
+         libdir=\${exec_prefix}/lib
+         includedir=\${prefix}/include
+         Name: pdfium
+         Description: pdfium
+         Version: 4290
+         Requires:
+         Libs: -L\${libdir} -lpdfium
+         Cflags: -I\${includedir}
+    EOF
 
 If PDFium is not detected, libvips will look for poppler-glib instead.