Add detailed smarty cache documentation to config
Add detailed smarty cache documentation to config

Instead of just making it availble document the smarty cache feature.

It might work for users, but it's advised to rely on the memcache
instead.

Fixes #309

shreeneve/test,sixxkilur/php-mpos,mmitech/php-mpos,studio666/php-mpos,evgenyponomarev/pool,CoinHashMe/MPOS-SSO,mculp/chunky-mpos,machinecoin-project/php-mpos,ychaim/php-mpos,studio666/php-mpos,mmitech/php-mpos,nimblecoin/web,MPOS/php-mpos,sasselin/xcoin-mpos,sasselin/xcoin-mpos,sasselin/xcoin-mpos,bankonme/php-mpos,MPOS/php-mpos,machinecoin-project/php-mpos,machinecoin-project/php-mpos,CoinHashMe/MPOS-SSO,bankonme/php-mpos,CoinHashMe/MPOS-SSO,ychaim/php-mpos,UNOMP/chunky-mpos,mmitech/php-mpos,mculp/chunky-mpos,BlueDragon747/php-mpos,BlueDragon747/php-mpos,xisi/php-mpos,nimblecoin/web,BlueDragon747/php-mpos,xisi/php-mpos,UNOMP/chunky-mpos,ychaim/php-mpos,MPOS/php-mpos,mculp/chunky-mpos,UNOMP/chunky-mpos,UNOMP/chunky-mpos,sixxkilur/php-mpos,CoinHashMe/MPOS-SSO,bankonme/php-mpos,xisi/php-mpos,nimblecoin/web,mculp/chunky-mpos,studio666/php-mpos,CoinHashMe/MPOS-SSO,shreeneve/test,sixxkilur/php-mpos,shreeneve/test,evgenyponomarev/pool,evgenyponomarev/pool