Added imagemagick notes to the knowledge base

knowledge base/imagemagick.md

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+# ImageMagick
+
+Components:
+
+- `convert`: image conversion tool
+
+## TL;DR
+
+```shell
+# scale an image to 50% its original size
+convert IMG_20200117_135049.jpg -adaptive-resize 50% IMG_20200117_135049_resized.jpg
+
+# create a gif using images
+magick *.jpg images.gif
+
+# convert n images to individual pdf pages
+magick *.jpg +adjoin page-%d.pdf
+
+# convert n images to a single pdf document
+magick *.png out.pdf
+```
+
+## Further readings
+
+- [Website]
+- [cheat.sh/convert]
+- [Converting Multiple Images into a PDF File]
+
+[cheat.sh/convert]: https://cheat.sh/convert
+[website]: https://imagemagick.org
+[converting multiple images into a pdf file]: https://legacy.imagemagick.org/discourse-server/viewtopic.php?p=144157&sid=e7706233f81874af86ffbbf3e57b1e76#p144157