note on updating existing source (#18409)

Summary:
Fixes https://github.com/pytorch/pytorch/issues/18388
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18409

Differential Revision: D14597666

Pulled By: soumith

fbshipit-source-id: 156104c0cd19da06f6f96a225228d1e8cf831af1

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 25372f1..84d68eb 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -36,6 +36,17 @@ git clone https://github.com/pytorch/pytorch
 cd pytorch
 ```
 
+2.1. If you already have PyTorch from source, update it:
+
+```bash
+git pull --rebase
+git submodule sync --recursive
+git submodule update --init --recursive
+```
+
+If you want to have no-op incremental rebuilds (which are fast), see the section below titled "Make no-op build fast."
+
+
 3. Install PyTorch in `develop` mode:
 
 A full set of instructions on installing PyTorch from source is here: