Explainer Updates

[mmccool]

• New discovery section content (main contribution as this was missing before)
• Adding discovery as a building block in the intro
• Adding hyperlinks in Scripting API section to be consistent with other sections
• Adding Scripting and Binding Templates as optional/informative building blocks in the summary
• Changing name "WoT Security and Privacy Considerations" to "WoT Security and Privacy Guidelines"
• Grammatically treating "Security" and "Privacy" as two different things in certain places
• And various other small fixes, including getting rid of some extraneous verbiage and breaking up long sentences.

Note this is a blocker for proceeding with horizontal review. Please review and I will attempt to deal with any feedback ASAP so we can reach consensus.

[sebastiankb]

looks ok for me. Just asking for a small change request.

[mlagally]

Please incorporate the proposed changes.