Update README.md (#10705)

typo error: replaced single quotation mark with backticks.

ppstructure/kie/README.md

@@ -87,7 +87,7 @@ Demo results for SER task are as follows.
 
 Boxes of different colors in the image represent different categories.
 
-The invoice and application form images have three categories: `request`, `answer` and `header`. The `question` and 'answer' can be used to extract the relationship.
+The invoice and application form images have three categories: `request`, `answer` and `header`. The `question` and `answer` can be used to extract the relationship.
 
 For the ID card image, the model can directly identify the key information such as `name`, `gender`, `nationality`, so that the subsequent relationship extraction process is not required, and the key information extraction task can be completed using only on model.