Redmine#3864: describe the policy framework

(cherry picked from commit 6153e83d6b6e10a1916d40920f73b3837c584d46)
Redmine#3864: adjust docs for 3.6.x
Redmine#5730: add more platforms to default software directories

(cherry picked from commit 4b2b06815b18c09b43c960e1321ba4cc834dfa4e)