Added a couple of tips

1) Add as many SVN -> Git author mappings as possible
2) put the 'etch = +refs/svn/map:refs/notes/commits' a seperate line
Added note on running register subcommand with correct environment

use the -E option to sudo that any settinsg for JAVA_HOME get passed in
Merge pull request #1 from alecthegeek/subgit-book-remote

Added a couple of tips