clarify LICENSE
clarify LICENSE

make clear the viral nature does not extend to other network services
edx/XBlock,jamiefolsom/xblock-sdk,Pilou81715/hackathon_edX,Pilou81715/hackathon_edX,jamiefolsom/xblock-sdk,4eek/XBlock,stvstnfrd/xblock-sdk,Lyla-Fischer/xblock-sdk,mitodl/XBlock,nagyistoce/edx-XBlock,EDUlib/XBlock,edx/XBlock,jamiefolsom/xblock-sdk,Lyla-Fischer/xblock-sdk,nagyistoce/edx-xblock-sdk,edx/xblock-sdk,edx-solutions/xblock-sdk,4eek/XBlock,lovehhf/xblock-sdk,nagyistoce/edx-xblock-sdk,Lyla-Fischer/xblock-sdk,edx/xblock-sdk,cpennington/XBlock,lovehhf/xblock-sdk,Pilou81715/hackathon_edX,jamiefolsom/xblock-sdk,EDUlib/XBlock,lovehhf/xblock-sdk,edx-solutions/xblock-sdk,stvstnfrd/xblock-sdk,edx-solutions/XBlock,edx-solutions/xblock-sdk,Pilou81715/hackathon_edX,lovehhf/xblock-sdk,lovehhf/XBlock,open-craft/XBlock,mitodl/XBlock,nagyistoce/edx-xblock-sdk,cpennington/XBlock,nagyistoce/edx-xblock-sdk,dcadams/xblock-sdk,dcadams/xblock-sdk,edx-solutions/xblock-sdk,nagyistoce/edx-XBlock,open-craft/XBlock,stvstnfrd/xblock-sdk,lovehhf/XBlock,edx/xblock-sdk,edx-solutions/XBlock,dcadams/xblock-sdk,cpennington/XBlock