Add Flutter as a Skia customer

Change-Id: Ida222fcd4fafc7fc6259f5f5943eff8d0475236f
No-Try: true
Docs-Preview: https://skia.org/?cl=302081
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/302081
Auto-Submit: Yuqian Li <[email protected]>
Commit-Queue: Heather Miller <[email protected]>
Reviewed-by: Heather Miller <[email protected]>

Author: liyuqian

site/index.md

@@ -3,8 +3,8 @@ Skia Graphics Library
 
 Skia is an open source 2D graphics library which provides common APIs that work
 across a variety of hardware and software platforms.  It serves as the graphics
-engine for Google Chrome and Chrome OS, Android, Mozilla Firefox and Firefox
-OS, and many other products.
+engine for Google Chrome and Chrome OS, Android, Flutter, Mozilla Firefox and
+Firefox OS, and many other products.
 
 Skia is sponsored and managed by Google, but is available for use by anyone
 under the BSD Free Software License.  While engineering of the core components

site/index_zh.md

@@ -2,7 +2,7 @@ Skia图形库
 =====================
 
 Skia是一个开源的二维图形库，提供各种常用的API，并可在多种软硬件平台上运行。谷歌Chrome浏览器、Chrome
-OS、安卓、火狐浏览器、火狐操作系统以及其它许多产品都使用它作为图形引擎。
+OS、安卓、Flutter、火狐浏览器、火狐操作系统以及其它许多产品都使用它作为图形引擎。
 
 <!-- Skia is an open source 2D graphics library which provides common APIs that work
 across a variety of hardware and software platforms.  It serves as the graphics