update e4s installation docs

[shahzebsiddiqui]

This page needs to be updated https://e4s-project.github.io/installation.html

It would be nice if the page was better formatted to suit code format instead of scrolling from left to right which is quite annoying.

Anyhow, I ran into issue when running

salloc -N 2 -q interactive -t 00:30:00 --image=exascaleproject/sdk:AHM19 -C haswell -L SCRATCH
srun -n 32 shifter  -- /bin/bash  -c 'unset CRAYPE_VERSION;  . /etc/bashrc ; spack load   trilinos hypre parmetis hdf5 metis openblas superlu zlib netcdf matio boost@1.66.0 scalapack suite-sparse tau; spack unload openmpi mpich; ./Zoltan'

The issue is Zoltan is not in my current directory, if this package is provided by image then the path should be updated. Based on my discussion with Sameer the image needs to be updated so all examples for docker, singularity, shifter and charlie cloud would need to be reflected using a new image.

Right now i am unable to locate Zoltan so the srun command will fail

[shahzebsiddiqui]

@wspear @sameershende @eugeneswalker you may want to update the installation docs.