Add wasm build instructions to documentation

Author: mcbarton

docs/source/InstallationAndUsage.rst

@@ -1,7 +1,7 @@
 Installation And Usage
 --------------------
 
-Installation from source
+Installation from source (non wasm build instructions)
 ========================
 
 To ensure that the installation works, it is preferable to install `xeus-cpp` in a
@@ -42,6 +42,59 @@ with a custom installation prefix if need be)
     -D CMAKE_INSTALL_LIBDIR=lib
     make && make install
 
+Installation within a mamba environment (wasm build instructions)
+========================
+
+These instructions will assume you have cmake installed on your system. First clone the repository, and move into that directory
+.. code-block:: bash
+    git clone --depth=1 https://github.com/compiler-research/xeus-cpp.git
+    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
+
+.. code-block:: bash
+    cd $HOME
+    git clone https://github.com/emscripten-core/emsdk.git
+    cd emsdk
+    ./emsdk install 3.1.45
+    ./emsdk activate 3.1.45
+    source $HOME/emsdk/emsdk_env.sh
+
+
+You are now in a position to build the xeus-cpp kernel. You build it by executing the following
+
+.. code-block:: bash
+    micromamba create -f environment-wasm-host.yml --platform=emscripten-wasm32
+    mkdir build
+    pushd build
+    export PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-host 
+    export CMAKE_PREFIX_PATH=$PREFIX
+    export CMAKE_SYSTEM_PREFIX_PATH=$PREFIX
+
+    emcmake cmake \
+            -DCMAKE_BUILD_TYPE=Release                        \
+            -DCMAKE_PREFIX_PATH=$PREFIX                       \
+            -DCMAKE_INSTALL_PREFIX=$PREFIX                    \
+            -DXEUS_CPP_EMSCRIPTEN_WASM_BUILD=ON               \
+            -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ON            \
+            ..
+    emmake make install
+
+
+To build Jupyter Lite with this kernel without creating a website you can execute the following
+
+.. code-block:: bash
+    micromamba create -n xeus-lite-host jupyterlite-core
+    micromamba activate xeus-lite-host
+    python -m pip install jupyterlite-xeus
+    jupyter lite build --XeusAddon.prefix=$PREFIX
+
+Once the Jupyter Lite site has built you can test the website locally by executing
+
+.. code-block:: bash
+    jupyter lite serve --XeusAddon.prefix=$PREFIX
+
 Installing from conda-forge
 ===========================