add git-lfs

git-lfs.md

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+# Git LFS
+
+Read [Git Large File Storage](https://git-lfs.github.com/).
+
+After install, run this once:
+
+```sh
+git lfs install
+```
+
+Select the file types for Git LFS to manage:
+
+```sh
+git lfs track "*.pdf"
+```
+
+Make sure `.gitattributes` is tracked:
+
+```sh
+git add .gitattributes
+```
+
+From now on, clone repository will call Git LFS if possible.