Document fill prop

docs/content/packages/react.mdx

@@ -15,6 +15,7 @@ npm install @primer/octicons-react
 ## Usage
 
 ### Icons
+
 The `@primer/octicons-react` module exports individual icons as [named
 exports](https://ponyfoo.com/articles/es6-modules-in-depth#named-exports). This
 allows you to import only the icons that you need without blowing up your
@@ -34,6 +35,7 @@ If you were to compile this example with a tool that supports [tree-shaking][]
 the "zap" and "beaker" icons.
 
 ### Vertical alignment
+
 By default the octicons have `vertical-align: text-bottom;` applied as inline
 styles. You can change the alignment via the `verticalAlign` prop, which can be
 either `middle`, `text-bottom`, `text-top`, or `top`.
@@ -43,13 +45,13 @@ import {RepoIcon} from '@primer/octicons-react'
 
 export default () => (
   <h1>
-    <RepoIcon verticalAlign='middle' /> github/github
+    <RepoIcon verticalAlign="middle" /> github/github
   </h1>
 )
 ```
 
-
 ### `aria-label`
+
 You have the option of adding accessibility information to the icon with the
 [`aria-label` attribute][aria-label] via the `aria-label` prop.
 
@@ -64,25 +66,42 @@ export default () => (
 )
 ```
 
-
 ### Sizes
+
 The `size` prop takes `small`, `medium`, and `large` values that can be used to
 render octicons at standard sizes:
 
-| Prop | Rendered Size |
-| :- | :- |
-| `size='small'` | 16px height by `computed` width |
+| Prop            | Rendered Size                   |
+| :-------------- | :------------------------------ |
+| `size='small'`  | 16px height by `computed` width |
 | `size='medium'` | 32px height by `computed` width |
-| `size='large'` | 64px height by `computed` width |
+| `size='large'`  | 64px height by `computed` width |
 
 ```js
 // Example usage
 import {LogoGithubIcon} from '@primer/octicons-react'
 
 export default () => (
   <h1>
-    <a href='https://github.com'>
-      <LogoGithubIcon size='large' aria-label='GitHub'/>
+    <a href="https://github.com">
+      <LogoGithubIcon size="large" aria-label="GitHub" />
+    </a>
+  </h1>
+)
+```
+
+### Fill
+
+The `fill` prop takes a string value that can be used to set the color of the icon.
+By default, `fill` is set to `currentColor`, which means it inherits it's parent's text color.
+
+```js
+// Example usage
+import {LogoGithub} from '@primer/octicons-react'
+export default () => (
+  <h1>
+    <a href="https://github.com">
+      <LogoGithubIcon fill="#f00" />
     </a>
   </h1>
 )