Clarify process creation and submission of DCPs

[s-ben]

There is occasional confusion about the process of creating a DCP, particularly from an "outsider" perspective, as illustrated in this recent chat. In particular, @davecgh points out a couple common misperceptions:

a) You're required to go through Politeia to contribute
b) You can use Politeia to direct the efforts of Decred contractors

In addition, there is confusion over how an "outside" party (developers not paid by the Treasury) would submit a DCP. E.g. how would a dcrd binary with the proposed changes be distributed, without the release going through Decred's normal process for distributing updates (answer: burden is on the proposer to rally stakeholders running full nodes to install their binary with the change).

As pointed out by @RichardRed0x, we should also try and clarify that one doesn't need stakeholder approval to work on anything. Typical FOSS model applies.

I see several places that could be updated to make this more clear:

• Introduction to Decred Governance - NOTE: this page is being updated here.
• Consensus Rule Voting
• DCP spec - could update intro text.

[imestin]

#996