added documentation about using custom font

Author: Cerem Cem ASLAN

doc/Adding_a_custom_font.md

@@ -0,0 +1,30 @@
+# Setup 
+
+1. Download your font file (eg. "7segment.ttf" from https://torinak.com/font/7-segment)
+
+2. Upload the font file to your website: 
+
+    1. Create a folder named `assets`.
+    2. Move your font file into the `assets` folder. 
+       Contents of this folder will directly be copied to the root of your build dir.
+
+3. Create a `.css` file that declares the font: 
+
+    ```css
+    @font-face {
+        font-family: "7Segment";
+        src: url("/7segment.ttf");
+    }
+
+    .seven-segment {
+        font-family: "7Segment";
+        letter-spacing: 2px;
+    }
+    ```
+
+# Use the font in your HTML
+
+```pug
+.ui.tag.black.big.label 
+    span.seven-segment(style="color: red") {{read}}
+```