Prerequisites - time and the LD_LIBRARY_PATH

[l0k18]

I am working with an Arch Linux system, and I encountered two issues when building this code.

First was setting the LD_LIBRARY_PATH, for this, the command, which I found in another issue:

export LD_LIBRARY_PATH=$PWD

The second prerequisite was the 'time' command. On Arch Linux the function exists, I'm not 100% certain, but I think, within bash itself, and so the makefile was unable to run the timing tests until I installed the package with pacman -S time.

There is no build instructions in the README.md and I think these two things should be added in order to complete the documentation.

I found there is a note about in the Makefile...

[tromp]

Build instructions added and 'time's for common targets removed