Update docs/build.rst
Update docs/build.rst

Add information to install mongodb 2.2>= on ubuntu
ggarnier/tsuru,hcxiong/tsuru,kgrvamsi/tsuru,cezarsa/tsuru,ArxdSilva/tsuru,gwmoura/tsuru,cgvarela/tsuru,jblancett/tsuru,jblancett/tsuru,jblancett/tsuru,firebitsbr/tsuru,gciotta/tsuru,4eek/tsuru,cezarsa/tsuru,tuxmonteiro/tsuru,tsuru/tsuru,ArxdSilva/tsuru,guilhermebr/tsuru,cezarsa/tsuru,hugoantunes/tsuru,guilhermebr/tsuru,Endika/tsuru,guilhermebr/tsuru,cezarsa/tsuru,gciotta/tsuru,RichardKnop/tsuru,tuxmonteiro/tsuru,kgrvamsi/tsuru,ArxdSilva/tsuru,guilhermebr/tsuru,RichardKnop/tsuru,tsuru/tsuru,cgvarela/tsuru,gwmoura/tsuru,firebitsbr/tsuru,cgvarela/tsuru,firebitsbr/tsuru,4eek/tsuru,Endika/tsuru,hcxiong/tsuru,RichardKnop/tsuru,mderaldo/tsuru,kgrvamsi/tsuru,tsuru/tsuru,gwmoura/tsuru,tsuru/tsuru,tuxmonteiro/tsuru,ggarnier/tsuru,hcxiong/tsuru,ggarnier/tsuru,ggarnier/tsuru,hugoantunes/tsuru,mderaldo/tsuru,gciotta/tsuru,ArxdSilva/tsuru,Endika/tsuru,mderaldo/tsuru,4eek/tsuru