Add build instructions to Readme?

[Zuikkis]

Hi!

This is a great utility, but very difficult to install if you have little experience in Java and/or Maven.

Anyway, this seems to be the correct procedure:

sudo apt install jre-default maven git
git clone https://github.com/cameronhunter/glacier-cli.git
cd glacier-cli
mvn package

And you have the executables in target/glacier-cli/bin directory!

Works fine except it doesn't find the credentials from ~/.aws/credentials file, or from the env variables. But I fixed that with a small script that parses credentials and then runs glacier with correct -a -s -r parameters:

#!/bin/bash

aws_access_key_id=`grep aws_access_key_id ~/.aws/credentials|cut -d= -f2`
aws_secret_access_key=`grep aws_secret_access_key ~/.aws/credentials|cut -d= -f2`
aws_region=`grep region ~/.aws/config|cut -d= -f2`

glacier-cli/target/glacier-cli/bin/glacier -a $aws_access_key_id -s $aws_secret_access_key -r $aws_region $@