Update git-xet brew installation instruction (#2017)

Users need to run `git-xet install` after `brew install git-xet`. This instruction is printed out at the end of the `brew install git-xet` step and people may not pay attention to that.

Author: seanses

docs/hub/xet/using-xet-storage.md

@@ -44,6 +44,7 @@ Install [Git](https://git-scm.com/) and [Git LFS](https://git-lfs.com/).
    ```
    brew tap huggingface/tap
    brew install git-xet
+   git-xet install
    ```
 
   To verify the installation, run:
@@ -122,4 +123,4 @@ When uploading or downloading in Git or Python:
 
 While Xet brings fine-grained deduplication and enhanced performance to Git-based storage, some features and platform compatibilities are still in development. As a result, keep the following constraints in mind when working with a Xet-enabled repository:
 
-- **64-bit systems only**: Both `hf_xet` and Git Xet currently require a 64-bit architecture; 32-bit systems are not supported.
+- **64-bit systems only**: Both `hf_xet` and Git Xet currently require a 64-bit architecture; 32-bit systems are not supported.