Added basic info about GIMP as another, open source, designer option. (#29464)

* Added basic info about GIMP as another open source designer option.

* made GIMP lowercase in folder path

guide/english/designer-tools/gimp/index.md

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+---
+title: GIMP
+---
+
+## GIMP
+
+Gimp is an acronym for GNU Image Manipulation Program. It's also open source and avaliable on Linux, OS X and Windows. 
+
+
+### Why Should I Switch To GIMP?
+
+- As I mentioned earlier it's FREE. The upgrades are also free!
+- It uses a fraction of the space most other image editing software. This also means you a can have it running in the background and it won't slow down anything else you might be busy with!
+- Also previously mentioned, it plays nicely with Mac/Windows/Unix. Particularly handy if you're collaborating with someone who uses a different operating system to you.
+- It doesn't discriminate against your machine whether it's 8 years old or brand spanking new, you can rest assured GIMP will run without a hitch.
+- Similarly to FreeCodeCamp's guides anyone can edit the core code or develop a Pugin.
+- GIMP has batch processing capabilities through automated actions. If you're a photographer I'm sure the angels in your head just sang.
+- You can open, edit and save Photoshop's native PSD file format in GIMP. Again, something super handy for collaborative work.
+- If you're used to the layout of Photoshop you can easily replicate its look and feel (as well as keyboard shortcuts) in GIMP.
+
+
+#### More Information
+
+- [GIMP] (https://www.gimp.org/)
+- [Download GIMP] (https://www.gimp.org/downloads/)
+- [GIMP Tutorials] (https://www.gimp.org/tutorials/)
+- [GIMP Wiki] (http://wiki.gimp.org/)
+- [GIMP FAQ] (https://www.gimp.org/docs/userfaq.html)