Update docs/mxnet/mxnet_backend_optimizer.md

Co-authored-by: Jake Lee <[email protected]>

Author: lanking520

docs/mxnet/mxnet_backend_optimizer.md

@@ -10,7 +10,7 @@ of the Criteria.
 ```
 
 After a name is passed, DJL will try to find the party library from
- the environment variable called `MXNET_EXTRA_LIBRARY_PATH`. User are required to
+ the environment variable called `MXNET_EXTRA_LIBRARY_PATH`. Users are required to
 set this environment variable to locate the library.  After that, you should see the messages from the inference to see if the library is enabled.
 
 Here is a list of supporting backend optimizers: