add credits for contributors

[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Davis | wc -l
1144
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Alice | wc -l
2944
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Galkin | wc -l
2649
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Steve | wc -l
4662
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Khalsa | wc -l
511
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Rama | wc -l
0
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Chagnon | wc -l
1258
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Richman | wc -l
1108
[~/dev/weatherbill/projects/docbrown]$ find -iname '*.clj' -exec git blame {} \; | grep Silva | wc -l
405
Merge pull request #2 from aliceliang/master

add credits for contributors