mention git clone --depth

Author: y21

Diff for: src/building/how-to-build-and-run.md

@@ -24,6 +24,27 @@ git clone https://github.com/rust-lang/rust.git
 cd rust
 ```
 
+### Shallow clone the repository
+
+Due to the size of the repository, cloning on a slower internet connection can take a long time.
+To sidestep this, you can use the `--depth N` option with the `git clone` command.
+This instructs `git` to perform a "shallow clone", cloning the repository but truncating it to the last `N` commits.
+
+Passing `--depth 1` tells `git` to clone the repository but truncate the history to the latest commit
+that is on the `master` branch, which is usually fine for browsing the source code or building the compiler.
+
+```bash
+git clone --depth 1 https://github.com/rust-lang/rust.git
+cd rust
+```
+
+> **NOTE**: A shallow clone limits which `git` commands can be run.
+> If you intend to work on and contribute to the compiler, it is
+> generally recommended to fully clone the repository [as shown above](#get-the-source-code).
+> 
+> For example, `git bisect` and `git blame` require access to the commit history,
+> so they don't work if the repository was cloned with `--depth 1`.
+
 ## What is `x.py`?
 
 `x.py` is the build tool for the `rust` repository. It can build docs, run tests, and compile the