Add info about math expression support on numeric fields

Author: dacap

new-sprite.md

@@ -4,10 +4,20 @@ You can create a new sprite from *File > New* menu (<kbd>Ctrl+N</kbd> or <kbd>
 
 ![New sprite dialog](new-sprite/newsprite.png)
 
-Here you select the sprite dimension (in pixels), its
-[color mode](color-mode.md), and the default background color.
+Here you select the sprite:
+
+* dimension (in pixels),
+* its [color mode](color-mode.md), and
+* the default background color.
+
 The sprite is created with a specific [palette by default](default-palette.md).
 
+### Math in Numeric Fields
+
+[Numeric fields](numeric-field.md) like *Width* and *Height* can evaluate little math expressions:
+
+![Math demo in numeric field](numeric-field/math.gif)
+
 ## New Sprite from Selection
 
 You can create a new sprite from the active selection using
@@ -19,4 +29,5 @@ You can create a new sprite from the active selection using
 
 **SEE ALSO**
 
-[Color Mode](color-mode.md)
+[Color Mode](color-mode.md) |
+[Default Palette](default-palette.md)

numeric-field.md

@@ -0,0 +1,12 @@
+# Numeric Field
+
+Numeric fields on Aseprite can evaluate simple math expressions:
+
+![Math demo in numeric field](numeric-field/math.gif)
+
+---
+
+**SEE ALSO**
+
+[New Sprite](new-sprite.md) |
+[Issue #1762](https://github.com/aseprite/aseprite/issues/1762)