Update instructions to include adding Rust to PATH

Current instructions do not include a callout to adding Rust to the PATH. While this included in the installer output and technically happens automatically after login, you can still miss it if you are trying to use Rust right away.

second-edition/src/ch01-01-installation.md

@@ -30,6 +30,19 @@ Rust is installed now. Great!
 Of course, if you disapprove of the `curl | sh` pattern, you can download, inspect
 and run the script however you like.
 
+The installation script automatically adds Rust to your system PATH after your next login. 
+If you want to start using Rust right away, run the following command in terminal:
+
+```text
+source $HOME/.cargo/env
+```
+
+Alternatively, add the following line to your `~/.bash_profile`:
+
+```text
+export PATH="$HOME/.cargo/bin:$PATH"
+```
+
 ### Installing on Windows
 
 On Windows, go to [https://rustup.rs](https://rustup.rs/)<!-- ignore --> and