docs/install/client: mention the PPA
docs/install/client: mention the PPA

Related to #555.

hcxiong/tsuru,mderaldo/tsuru,cezarsa/tsuru,RichardKnop/tsuru,hugoantunes/tsuru,ggarnier/tsuru,ggarnier/tsuru,cezarsa/tsuru,jblancett/tsuru,cezarsa/tsuru,cgvarela/tsuru,kgrvamsi/tsuru,ggarnier/tsuru,guilhermebr/tsuru,ArxdSilva/tsuru,hugoantunes/tsuru,tsuru/tsuru,gciotta/tsuru,jblancett/tsuru,Endika/tsuru,guilhermebr/tsuru,4eek/tsuru,gwmoura/tsuru,hcxiong/tsuru,cgvarela/tsuru,kgrvamsi/tsuru,tuxmonteiro/tsuru,tsuru/tsuru,RichardKnop/tsuru,ArxdSilva/tsuru,firebitsbr/tsuru,gciotta/tsuru,RichardKnop/tsuru,kgrvamsi/tsuru,gciotta/tsuru,ArxdSilva/tsuru,firebitsbr/tsuru,Endika/tsuru,Endika/tsuru,tsuru/tsuru,jblancett/tsuru,guilhermebr/tsuru,ggarnier/tsuru,hcxiong/tsuru,ArxdSilva/tsuru,gwmoura/tsuru,gwmoura/tsuru,tuxmonteiro/tsuru,cgvarela/tsuru,4eek/tsuru,guilhermebr/tsuru,mderaldo/tsuru,cezarsa/tsuru,tuxmonteiro/tsuru,tsuru/tsuru,mderaldo/tsuru,4eek/tsuru,firebitsbr/tsuru