add errorHandler documentation

docs/api.md

@@ -42,6 +42,7 @@ createWorker is a factory function that creates a tesseract worker, a worker is
   - `workerBlobURL` a boolean to define whether to use Blob URL for worker script, default: true
   - `gzip` a boolean to define whether the traineddata from the remote is gzipped, default: true
   - `logger` a function to log the progress, a quick example is `m => console.log(m)`
+  - `errorHandler` a function to handle worker errors, a quick example is `err => console.error(err)`
 
 
 **Examples:**
@@ -144,7 +145,7 @@ Worker.setParameters() set parameters for Tesseract API (using SetVariable()), i
 **Supported Paramters:**
 
 | name                        | type   | default value     | description                                                                                                                     |
-| ---- | ---- | ------------- | ----------- |
+| --------------------------- | ------ | ----------------- | ------------------------------------------------------------------------------------------------------------------------------- |
 | tessedit\_ocr\_engine\_mode | enum   | OEM.DEFAULT       | Check [HERE](https://github.com/tesseract-ocr/tesseract/blob/4.0.0/src/ccstruct/publictypes.h#L268) for definition of each mode |
 | tessedit\_pageseg\_mode     | enum   | PSM.SINGLE\_BLOCK | Check [HERE](https://github.com/tesseract-ocr/tesseract/blob/4.0.0/src/ccstruct/publictypes.h#L163) for definition of each mode |
 | tessedit\_char\_whitelist   | string | ''                | setting white list characters makes the result only contains these characters, useful the content in image is limited           |