readme: add installation instructions

[wihobbs]

Problem: there are no instructions in the readme for how to install flux-pmix.

Add some.

Fixes #112.

[garlick]

Thanks! I put a comment inline. I think two main take-aways are

• you can set PKG_CONFIG_PATH on the command line rather than exporting so it doesn't get set in someones interactive shell environment and affect other things they build
• PKG_CONFIG_PATH is used at configure time rather than make time IIUC

[garlick]

Usually the PKG_CONFIG_PATH needs to be set before ./configure?

I usually use a script similar to this

#!/bin/bash
PMIX_PREFIX=/opt/openpmix-4.2.2
OMPI_PREFIX=/opt/openmpi-5.0.0rc9
FLUX_CORE_PREFIX=/opt/flux-core-v0.46.1-54

PKG_CONFIG_PATH=$(pkg-config --variable pc_path pkg-config)
#PKG_CONFIG_PATH=${OMPI_PREFIX}/lib/pkgconfig:${PKG_CONFIG_PATH}
PKG_CONFIG_PATH=${PMIX_PREFIX}/lib/pkgconfig:${PKG_CONFIG_PATH}
PKG_CONFIG_PATH=${FLUX_CORE_PREFIX}/lib/pkgconfig:${PKG_CONFIG_PATH}

PKG_CONFIG_PATH=${PKG_CONFIG_PATH} \
     ./configure

[wihobbs]

Thanks for the reminder @garlick! I pushed up your script, with a small tweak to make it do the whole build + install, and install to the flux-core prefix. Let me know if that works.

[garlick]

@wihobbs did you want to fix this one and get it into the next release?

[garlick]

Thanks! Some comments inline for you to consider.

[garlick]

Maybe instead

To install flux-pmix with a side-installed flux-core so that the plugins provided by flux-pmix can be found on flux's default search paths, build and install to the same prefix. Here is an example script that uses pkg-config:

[wihobbs]

Sounds good, changed and pushed.

[wihobbs]

@garlick okay to set MWP?

[garlick]

Thanks - feel free to set MWP

[wihobbs]

Hmm, it looks like I don't have write access here to add labels.

[garlick]

Oh weird. I'll set it.