Update PR based on comment

Author: mcbarton

CONTRIBUTING.md

@@ -79,9 +79,9 @@ You are now in a position to build the xeus-cpp kernel. You build it by executin
 ```bash
 micromamba create -f environment-wasm-host.yml --platform=emscripten-wasm32
 mkdir build
-pushd build
-export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-host 
-export SYSROOT_PATH=$HOME/emsdk/upstream/emscripten/cache/sysroot
+cd build
+export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-build
+export SYSROOT_PATH=$PREFIX/opt/emsdk/upstream/emscripten/cache/sysroot
 
 emcmake cmake \
         -DCMAKE_BUILD_TYPE=Release                        \

README.md

@@ -80,9 +80,9 @@ You are now in a position to build the xeus-cpp kernel. You build it by executin
 ```bash
 micromamba create -f environment-wasm-host.yml --platform=emscripten-wasm32
 mkdir build
-pushd build
-export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-host 
-export SYSROOT_PATH=$HOME/emsdk/upstream/emscripten/cache/sysroot
+cd build
+export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-build
+export SYSROOT_PATH=$PREFIX/opt/emsdk/upstream/emscripten/cache/sysroot
 
 emcmake cmake \
         -DCMAKE_BUILD_TYPE=Release                        \

docs/source/InstallationAndUsage.rst

@@ -68,9 +68,9 @@ You are now in a position to build the xeus-cpp kernel. You build it by executin
 
     micromamba create -f environment-wasm-host.yml --platform=emscripten-wasm32
     mkdir build
-    pushd build
-    export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-host 
-    export SYSROOT_PATH=$HOME/emsdk/upstream/emscripten/cache/sysroot
+    cd build
+    export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-build
+    export SYSROOT_PATH=$PREFIX/opt/emsdk/upstream/emscripten/cache/sysroot
     emcmake cmake \
             -DCMAKE_BUILD_TYPE=Release                        \
             -DCMAKE_INSTALL_PREFIX=$PREFIX                    \