chore(kb/pdf): slightly update process to reduce pdf files size

knowledge base/ghostscript.md

@@ -18,6 +18,13 @@ gs -dNOPAUSE -dQUIET -dBATCH \
   -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dCompatibilityLevel=1.4 \
   -sOutputFile=path/to/small/file.pdf \
   path/to/massive/file.pdf
+gs \
+  -o /path/to/resized.pdf \
+  -sDEVICE=pdfwrite \
+  -dPDFFitPage \
+  -r300x300 \
+  -g2550x3300 \
+  /path/to/original.pdf
 ```
 
 ## Reduce the size of PDF files

knowledge base/imagemagick.md

@@ -16,6 +16,7 @@ Components:
 ```sh
 # Scale images to 50% its original size.
 magick convert -adaptive-resize '50%' 'in.jpg' 'out.jpg'
+ls -1 *.jpeg | parallel -qt magick convert -adaptive-resize '50%' {} scaled_{}
 
 # Create GIFs from single images.
 magick *.jpg 'out.gif'

knowledge base/mac os x/README.md

@@ -170,6 +170,8 @@ In the Preview app:
 1. Click the _Quartz Filter_ pop-up menu, then choose _Reduce File Size_.
 1. Click the _Export_ button.
 
+Alternatively, check [ImageMagick] or [Ghostscript] out.
+
 ## Manage tags
 
 Tags are stored both in a file's or folder's `com.apple.metadata:_kMDItemUserTags` extended attribute.
@@ -410,6 +412,7 @@ To use any of these key combinations, press and hold the keys immediately after
 
 <!-- Knowledge base -->
 [defaults]: defaults.md
+[ghostscript]: ../ghostscript.md
 [imagemagick]: ../imagemagick.md
 [jdberry/tag]: tag.md
 [little snitch]: little%20snitch.md