Create Contributing.mdx

docs/Contributing.mdx

@@ -0,0 +1,46 @@
+# Contributing guide
+
+Thank you for investing your time in contributing to this project! :sparkles:. 
+
+## New contributor guide
+
+To get an overview of the project, read the [README](README.md) and [wiki page](https://github.com/AdisonCavani/distro-grub-themes/wiki).
+
+### Project structure:
+
+```
+.
+├── assets                       - assets for creating background images
+|   ├── fonts                    - fonts used in each theme
+|   └── icons                    - icons that get copied to icons folder in every theme
+├── customize                    - non-compressed themes
+├── docs                         - documentation markdown files
+├── preview                      - preview images for README.md
+├── themes                       - compressed themes ready to install in .tar format
+└── themes.json                  - json file containing all themes definitions (used as database for wiki page)
+```
+
+### Workflow
+
+Folders that trigger new action/workflow:
+
+- assets
+- customize
+
+Every time you create new commit on master branch, github action bot will update all files (as defined in [this file](https://github.com/AdisonCavani/distro-grub-themes/blob/master/.github/workflows/update-content.yml)).  
+You can track your workflows [here](https://github.com/AdisonCavani/distro-grub-themes/actions).
+
+### Branches
+
+```
+├── master                       - main branch containing latest changes
+├── legacy                       - obsolete C# program, replaced by Github Actions workflow
+└── templates                    - PSD, phosothop templates for background images
+```
+
+### Frequently Asked Questions
+**Q**: Where are `psd` templates located?  
+**A**: Templates are located in [`templates`](https://github.com/AdisonCavani/distro-grub-themes/tree/templates) branch.
+
+**Q**: How can I edit `psd` template? I don't have Photoshop  
+**A**: You can import `psd` into GIMP, however this might cause to lose some Photoshop related data. I recommend to use [Photopea](https://www.photopea.com/) - free web-based Photoshop alternative.