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:**
@@ -143,17 +144,17 @@ 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 |
-| preserve\_interword\_spaces | string | '0' | '0' or '1', keeps the space between words |
-| tessjs\_create\_hocr | string | '1' | only 2 values, '0' or '1', when the value is '1', tesseract.js includes hocr in the result |
-| tessjs\_create\_tsv | string | '1' | only 2 values, '0' or '1', when the value is '1', tesseract.js includes tsv in the result |
-| tessjs\_create\_box | string | '0' | only 2 values, '0' or '1', when the value is '1', tesseract.js includes box in the result |
-| tessjs\_create\_unlv | string | '0' | only 2 values, '0' or '1', when the value is '1', tesseract.js includes unlv in the result |
-| tessjs\_create\_osd | string | '0' | only 2 values, '0' or '1', when the value is '1', tesseract.js includes osd in the result |
+| 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           |
+| preserve\_interword\_spaces | string | '0'               | '0' or '1', keeps the space between words                                                                                       |
+| tessjs\_create\_hocr        | string | '1'               | only 2 values, '0' or '1', when the value is '1', tesseract.js includes hocr in the result                                      |
+| tessjs\_create\_tsv         | string | '1'               | only 2 values, '0' or '1', when the value is '1', tesseract.js includes tsv in the result                                       |
+| tessjs\_create\_box         | string | '0'               | only 2 values, '0' or '1', when the value is '1', tesseract.js includes box in the result                                       |
+| tessjs\_create\_unlv        | string | '0'               | only 2 values, '0' or '1', when the value is '1', tesseract.js includes unlv in the result                                      |
+| tessjs\_create\_osd         | string | '0'               | only 2 values, '0' or '1', when the value is '1', tesseract.js includes osd in the result                                       |
 
 **Examples:**