Added docs from the pulp-2.4 branch.

This commit adds in the documentation changes that were present in the
pulp-2.4 branch that were not present in the 2.4-release branch. This
commit was generated using this command:

$ git diff 2.4-release..pulp-2.4 docs/
Should we change this to the "fork in your own github account" style?

Also I am fine with leaving this as-is for now and changing later if we want to discuss more on the email list.