Fix the emcc installation requirements

Author: juntyr

src/doc/rustc/src/platform-support/wasm32-unknown-emscripten.md

@@ -41,11 +41,8 @@ If you are only targeting the web and need to access web APIs, the
 ## Requirements
 
 This target is cross-compiled. The Emscripten compiler toolchain `emcc` must be
-installed to link WASM binaries for this target. Please refer to
-<https://emscripten.org/docs/getting_started/downloads.html> on how to get started
-with and install `emcc`.
-
-You can also build `emcc` from source with:
+installed to link WASM binaries for this target. You can install and activate
+`emcc` using:
 
 ```sh
 git clone https://github.com/emscripten-core/emsdk.git --depth 1
@@ -54,6 +51,9 @@ git clone https://github.com/emscripten-core/emsdk.git --depth 1
 source ./emsdk/emsdk_env.sh
 ```
 
+Please refer to <https://emscripten.org/docs/getting_started/downloads.html> for
+further details and instructions.
+
 ## Building the target
 
 Building this target can be done by: