Fixing base Docker image

[gentooza]

I have:

• Updated the alpine image from 3.4 to latest 3.19.
• Fixed certificates for wget, fixing #18
• Added some more dependencies as linux-headers, needed for compiling MPICH versions > 3.2, fixing #15.
• Updated the compiling flags of MPICH for being able to compile MPICH versions from 3.3 to 4.0.3.

I had to install nano, because get_hosts is not working for me and I had to edit manually the MPICH machinefile, I'll open an issue. I had to install bash because in last alpine versions test.sh execution breaks :-/ I don't know why. I'm not good with bash so I fixed doing this.

With this base image we can only compile now from 3.3 to 4.0.3

[NLKNguyen]

Nice! Could you add the version of MPICH to README? That seems to be a very important change for readers who come here from the research paper info. Also add version of Docker Engine/Compose that the current image is compatible with. We saw it being outdated before, so this will make future readers aware of potential Docker issue if they use much later versions than current.

Regarding sh or bash scripts, it's really a pain to work on them without shellcheck. Perhaps analyzing the shell scripts through it might shred some light.