Clarify nn_symbol documentation.
Clarify nn_symbol documentation.

Signed-off-by: Martin Sustrik <4dd6061be1198639e8b05ce4fd5ead7a0dcaa0f4@250bpm.com>

TTimo/nanomsg,snikulov/nanomsg,reqshark/nanomsg,tempbottle/nanomsg,potatogim/nanomsg,ttyangf/nanomsg,imp/nanomsg,zerotacg/nanomsg,pch957/nanomsg,pch957/nanomsg,ttyangf/nanomsg,modulexcite/nanomsg,JackDunaway/featherweight-nanomsg,kaostao/nanomsg,potatogim/nanomsg,imp/nanomsg,nirs/nanomsg,ttyangf/nanomsg,krafczyk/nanomsg,simplestbest/nanomsg,featherweight/ftw-kernel-nanomsg,thisco-de/nanomsg,JackDunaway/featherweight-nanomsg,smithed/nanomsg,pakozm/nanomsg,linearregression/nanomsg,wfxiang08/nanomsg,zerotacg/nanomsg,kaostao/nanomsg,tempbottle/nanomsg,cosin2008/nanomsg.NET,wirebirdlabs/featherweight-nanomsg,gdamore/mamomsg,modulexcite/nanomsg,smithed/nanomsg,nirs/nanomsg,reqshark/nanomsg,yan97ao/nanomsg,linearregression/nanomsg,gdamore/mamomsg,pakozm/nanomsg,cosin2008/nanomsg.NET,TTimo/nanomsg,pakozm/nanomsg,yan97ao/nanomsg,TTimo/nanomsg,potatogim/nanomsg,featherweight/ftw-kernel-nanomsg,JackDunaway/featherweight-nanomsg,hyperfact/nanomsg,imp/nanomsg,cosin2008/nanomsg.NET,modulexcite/nanomsg,TTimo/nanomsg,wfxiang08/nanomsg,ttyangf/nanomsg,wfxiang08/nanomsg,tempbottle/nanomsg,pch957/nanomsg,kaostao/nanomsg,linearregression/nanomsg,wirebirdlabs/featherweight-nanomsg,simplestbest/nanomsg,smithed/nanomsg,zerotacg/nanomsg,krafczyk/nanomsg,krafczyk/nanomsg,hyperfact/nanomsg,kaostao/nanomsg,reqshark/nanomsg,smithed/nanomsg,thisco-de/nanomsg,nirs/nanomsg,wirebirdlabs/featherweight-nanomsg,simplestbest/nanomsg,yan97ao/nanomsg,snikulov/nanomsg,gdamore/mamomsg,hyperfact/nanomsg