Fix #119: Indicate 403 forbidden error in known limitations

Author: Stichoza

README.md

@@ -167,12 +167,15 @@ In addition, `translate()` and `trans()` methods will return `null` if there is
 
 ## Known Limitations
 
- - `503 Service Unavailable` response:  
+ - `503 Service Unavailable` response:
    If you are getting this error, it is most likely that Google has banned your external IP address and/or [requires you to solve a CAPTCHA](https://github.com/Stichoza/google-translate-php/issues/18). This is not a bug in this package. Google has become stricter, and it seems like they keep lowering the number of allowed requests per IP per a certain amount of time. Try sending less requests to stay under the radar, or change your IP frequently ([for example using proxies](#http-client-configuration)). Please note that once an IP is banned, even if it's only temporary, the ban can last from a few minutes to more than 12-24 hours, as each case is different.
  - `429 Too Many Requests` response:
    This error is basically the same as explained above.
- - `413 Request Entity Too Large` response:  
+ - `413 Request Entity Too Large` response:
    This error means that your input string is too long. Google only allows a maximum of 5000 characters to be translated at once. If you want to translate a longer text, you can split it to shorter parts, and translate them one-by-one.
+ - `403 Forbidden` response:
+   This is not an issue with this package. Google Translate itself has some problems when it comes to translating some characters. See https://github.com/Stichoza/google-translate-php/issues/119#issuecomment-558078133
+
 
 ## Disclaimer