Fixed broken X AI Careers link

Current Link: https://x.ai/career -> 404 Error
New Link: https://x.ai/careers -> Works :-)

README.md

@@ -23,4 +23,4 @@ You should be seeing output from the language model.
 
 Due to the large size of the model (314B parameters), a multi-GPU machine is required to test the model with the example code.
 
-p.s. we're hiring: https://x.ai/career
+p.s. we're hiring: https://x.ai/careers