docs: Update MacOS prerequisites to require XCode
Some modules rely on Unix headers that are provided on MacOS via XCode,
adding some instructions here to explain installation steps.
Change-Id: Ib88988dec147dbc6443724e212f337ff625208d9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/29743
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Prashanth Swaminathan <prashanthsw@google.com>
diff --git a/docs/getting_started.md b/docs/getting_started.md
index 51702fa..5423d31 100644
--- a/docs/getting_started.md
+++ b/docs/getting_started.md
@@ -89,6 +89,13 @@
Make sure gcc is set to gcc-8.
**macOS**<br/>
+To start using Pigweed on MacOS, you'll need to install XCode. Download it
+via the App Store, then install the relevant tools from the command line.
+
+```bash
+xcode-select --install
+```
+
On macOS you may get SSL certificate errors with the system Python
installation. Run `sudo pip install certifi` to fix this. If you get SSL
errors with the Python from [Homebrew](https://brew.sh) try running the
