Update docs so LD_LIBRARY_PATH is defined

Author: mcbarton

CONTRIBUTING.md

@@ -38,6 +38,7 @@ micromamba activate xeus-cpp
 You are now in a position to install xeus-cpp into this environment. You can do this by executing
 
 ```bash
+export LD_LIBRARY_PATH="$CONDA_PREFIX/lib/:$LD_LIBRARY_PATH"
 mkdir build
 cd build
 cmake -D CMAKE_BUILD_TYPE=Release -D CMAKE_PREFIX_PATH=$CONDA_PREFIX -D CMAKE_INSTALL_PREFIX=$CONDA_PREFIX -D CMAKE_INSTALL_LIBDIR=lib ..

README.md

@@ -59,6 +59,7 @@ micromamba install jupyterlab -c conda-forge
 ```
 Now you can compile the kernel from the source by executing (replace `$CONDA_PREFIX` with a custom installation prefix if need be)
 ```bash
+export LD_LIBRARY_PATH="$CONDA_PREFIX/lib/:$LD_LIBRARY_PATH"
 mkdir build
 cd build
 cmake .. -D CMAKE_PREFIX_PATH=$CONDA_PREFIX -D CMAKE_INSTALL_PREFIX=$CONDA_PREFIX -D CMAKE_INSTALL_LIBDIR=lib

docs/source/InstallationAndUsage.rst

@@ -30,6 +30,7 @@ with a custom installation prefix if need be)
 
 .. code-block:: bash
 
+    export LD_LIBRARY_PATH="$CONDA_PREFIX/lib/:$LD_LIBRARY_PATH"
     mkdir build && cd build
     cmake .. -D CMAKE_PREFIX_PATH=$CONDA_PREFIX -D CMAKE_INSTALL_PREFIX=$CONDA_PREFIX 
     -D CMAKE_INSTALL_LIBDIR=lib