Improve handling spaces in example command (#6482)

README.md

@@ -283,7 +283,7 @@ To generate code with this image, you'll need to mount a local location as a vol
 Example:
 
 ```sh
-docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli generate \
+docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli generate \
     -i https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/2_0/petstore.yaml \
     -g go \
     -o /local/out/go