Fix emsk install and activate commands

Author: mcbarton

CONTRIBUTING.md

@@ -71,8 +71,8 @@ cd ./xeus-cpp
 You'll now want to make sure you're using emsdk version "3.1.45" and activate it. You can get this by executing the following
 ```bash
 git clone https://github.com/emscripten-core/emsdk.git $HOME/emsdk
-$HOME/emsdk install 3.1.45
-$HOME/emsdk activate 3.1.45
+$HOME/emsdk/emsdk install 3.1.45
+$HOME/emsdk/emsdk activate 3.1.45
 source $HOME/emsdk/emsdk_env.sh
 ```
 

README.md

@@ -72,8 +72,8 @@ cd ./xeus-cpp
 You'll now want to make sure you're using emsdk version "3.1.45" and activate it. You can get this by executing the following
 ```bash
 git clone https://github.com/emscripten-core/emsdk.git $HOME/emsdk
-$HOME/emsdk install 3.1.45
-$HOME/emsdk activate 3.1.45
+$HOME/emsdk/emsdk install 3.1.45
+$HOME/emsdk/emsdk activate 3.1.45
 source $HOME/emsdk/emsdk_env.sh
 ```
 

docs/source/InstallationAndUsage.rst

@@ -58,8 +58,8 @@ You'll now want to make sure you're using emsdk version "3.1.45" and activate it
 .. code-block:: bash
 
     git clone https://github.com/emscripten-core/emsdk.git $HOME/emsdk
-    $HOME/emsdk install 3.1.45
-    $HOME/emsdk activate 3.1.45
+    $HOME/emsdk/emsdk install 3.1.45
+    $HOME/emsdk/emsdk activate 3.1.45
     source $HOME/emsdk/emsdk_env.sh