Update README.md
Summary:
Fix broken link to [INSTALL.md]
`(INSTALL.md)`
>
`(https://github.com/facebookresearch/detectron2/blob/master/INSTALL.md)`
Pull Request resolved:
@@ -5,7 +5,7 @@ Documents in this directory are not meant to be read on github.
# Build the docs:
-1. Install detectron2 according to [INSTALL.md](INSTALL.md).
+1. Install detectron2 according to [INSTALL.md](https://github.com/facebookresearch/detectron2/blob/master/INSTALL.md).
2. Install additional libraries required to build docs:
- docutils==0.16
- Sphinx==3.0.0
