Adds a warning about the requirement to use Identity API 2.0

Object Storage is unaware of domains so ACLs cannot be enforced
when using Identity API 3.0

Change-Id: I6a1f8853e7cfcb5c4e8f789fa7fe8dfd6d3f7fdd
Closes-bug: 1299146
fixed typos found by topy in security-guide directory

Topy is available at https://github.com/intgr/topy.

Change-Id: I417dd9b40469364f787c719fb05a2576163121ea
Merge "fixed typos found by topy in security-guide directory"
Merge "Adds a warning about the requirement to use Identity API 2.0"