Add GIF format to documentation (#1035)

Author: hata6502

docs/image-format.md

@@ -2,7 +2,7 @@
 
 The main Tesseract.js functions (ex. recognize, detect) take an `image` parameter.  The image formats and data types supported are listed below. 
 
-Support Image Formats: **bmp, jpg, png, pbm, webp**
+Support Image Formats: **bmp, jpg, png, pbm, webp, gif \[non-animated\]**.
 
 For browser and Node, supported data types are:
  - string with base64 encoded image (fits `data:image\/([a-zA-Z]*);base64,([^"]*)` regexp)
@@ -15,4 +15,4 @@ For browser only, supported data types are:
 For Node only, supported data types are:
  - string containing a path to local image
 
-Note: images must be a supported image format **and** a supported data type.  For example, a buffer containing a png image is supported.  A buffer containing raw pixel data is not supported. 
+Note: images must be a supported image format **and** a supported data type.  For example, a buffer containing a png image is supported.  A buffer containing raw pixel data is not supported.