Update How_to_Load_Securities.rst
Update How_to_Load_Securities.rst

REQS-457 - Adding documentation on how to define a corporate bond security by directly specifying the required fields and optional attributes.
nssales/OG-Platform,codeaudit/OG-Platform,DevStreet/FinanceAnalytics,nssales/OG-Platform,codeaudit/OG-Platform,jerome79/OG-Platform,nssales/OG-Platform,ChinaQuants/OG-Platform,jerome79/OG-Platform,DevStreet/FinanceAnalytics,nssales/OG-Platform,DevStreet/FinanceAnalytics,jeorme/OG-Platform,ChinaQuants/OG-Platform,jerome79/OG-Platform,codeaudit/OG-Platform,ChinaQuants/OG-Platform,codeaudit/OG-Platform,jerome79/OG-Platform,jeorme/OG-Platform,DevStreet/FinanceAnalytics,ChinaQuants/OG-Platform,jeorme/OG-Platform,jeorme/OG-Platform