Update README.md

Indicate throttling issue.

README.md

@@ -2,6 +2,10 @@
 
 `wikihow2zim` is an [OpenZIM](https://openzim.org) scraper to create offline versions of [wikiHow](https://www.wikihow.com) websites, in all its supported languages.
 
+
+| :zap:        Scraper is known to have a very significant issue linked to throttling (https://github.com/openzim/wikihow/issues/150)   |
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