updated contributing guidelines

CONTRIBUTING.md

@@ -9,6 +9,11 @@ These guidelines were written to inform you about all the things needed for icon
 
 1. fork the [Cryptocoins repo](https://github.com/AllienWorks/cryptocoins)
 2. add/edit/rename icons in the `SVG/` folder
+   - when adding new coins, be sure to keep the SVG canvas dimensions the same as other icons'
+   - keep the visual consistency of icons (paddings from borders etc.)
+   - if needed, we prefer a bit stylized icons rather than 100% original logos (for example if some lines won't be visible on small sizes, make them thicker); some degree of stylization is accepted as well
+   - final icon should be monochrome (black) SVG, single layer (don't use white shapes anywhere in the SVG!)
+   - use the correct naming of `ICON` and `ICON-alt` (see other icons)
 3. generate the webfont via running `gulp`
    - you'll need to `yarn install` or `npm install` first
    - get [yarn](https://yarnpkg.com/en/) or [npm](https://www.npmjs.com/)

README.md

@@ -48,6 +48,11 @@ Initial release contains just a fraction of Altcoins. If you're missing your coi
 **This is all completely voluntary work**, so if you want to support my efforts _or_ speed up the addition of your coin, [please donate](https://allien.work/donate). Donation addresses are found below (if you don't see your coin, let me know and I'll send the address afterwards).
 
 
+## For Contributors
+
+Please see [Contributing guidelines](CONTRIBUTING.md) before submitting your PRs, thanks!
+
+
 ## Author
 
 **Martin Allien**