Revise linker installation instructions. Fixes #2151.

src/ch01-01-installation.md

@@ -39,13 +39,21 @@ for your password. If the install is successful, the following line will appear:
 Rust is installed now. Great!
 ```
 
-Additionally, you’ll need a linker of some kind. It’s likely one is already
-installed, but when you try to compile a Rust program and get errors indicating
-that a linker could not execute, that means a linker isn’t installed on your
-system and you’ll need to install one manually. C compilers usually come with
-the correct linker. Check your platform’s documentation for how to install a C
-compiler. Also, some common Rust packages depend on C code and will need a C
-compiler. Therefore, it might be worth installing one now.
+You will also need a linker, which is a program that Rust uses to join its
+compiled outputs into one file. It is likely you already have one. If you get
+linker errors, you should install a C compiler, which will typically include a
+linker. A C compiler is also useful because some common Rust packages depend on
+C code and will need a C compiler.
+
+On macOS, you can get a C compiler by running:
+
+```console
+$ xcode-select --install
+```
+
+Linux users should generally install GCC or Clang, according to their
+distribution's documentation. For example, if you use Ubuntu, you can install
+the `build-essential` package.
 
 ### Installing `rustup` on Windows