[doc] [distributed] fix typo (#39264)

Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/39264

Differential Revision: D21791426

Pulled By: mrshenli

fbshipit-source-id: c3aa8fda1893aa3c0f9ad3db7da25f1ee80303e8
diff --git a/torch/distributed/distributed_c10d.py b/torch/distributed/distributed_c10d.py
index 4682b56..bc1fab3 100644
--- a/torch/distributed/distributed_c10d.py
+++ b/torch/distributed/distributed_c10d.py
@@ -370,7 +370,7 @@
             is set to 1.
         group_name (str, optional, deprecated): Group name.
 
-    To enable ``backend == Backend.MPI``, PyTorch needs to built from source
+    To enable ``backend == Backend.MPI``, PyTorch needs to be built from source
     on a system that supports MPI.
 
     """