fix conda install cmd in INSTALL.md

Summary: Pull Request resolved: facebookresearch#8

Differential Revision: D19556466

Pulled By: nikhilaravi

fbshipit-source-id: 26aa361882b688e7cd159e0d7d8cfad37d0049c1

Author: chenyuntc

INSTALL.md

@@ -52,7 +52,7 @@ After installing the above dependencies, run one of the following commands:
 
 ```
 # Anaconda Cloud
-conda install pytorch3d
+conda install pytorch3d -c pytorch3d
 ```
 
 ### 2. Install from GitHub