rename and re-draft doc

Author: tvarney13

internal/dev_server/manifesto.md

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+# Dev Server Vision Doc
+
+This doc lays out our vision for what `dev-server` is supposed to do, and why this is the case.
+
+## Purpose of the Dev Server
+
+First and foremost, `dev-server` is meant as a replacement for local dev and CI environments. Other use cases may exist (and don't hestitate to ask if you think you have one!), but since a `dev-server` environment lacks any targeting, it is best suited to situations where there is only 1 user for the whole environment.
+
+We implemented it this way in order to solve a problem common both internally and amongst our userbase where an environment would get created per developer on a project as well as per CI build. As you could expect, this becomes exponentially harder to maintain as the number of environments scales both technically and from a process perspective - something has to clear out those environments after all!
+
+Another intentional design decision was the choice not to allow the creation of local-only flags. A running `dev-server` can only pull from a real environment. From there, you can override the served value for your local environment.
+
+We chose to do this in order to minimize any surprises as your code moves from local / CI to a prod / prod-like environment. In our experience, the greatest source of such surprises has been drift between the configuration of a developer's LD environment and our Staging environment. Unless a developer is constantly making sure their flag state matches higher environments as closely as possible, flag state drifts until their local development environment starts to break, neccessitating a painful process of reconciling flag state.
+
+Lastly, we highly recommend not using `dev-server` for environments with prod-level traffic. As we designed this with local dev in mind, something will definitely break if you try to use this for that level of load.
+
+With that said, it's our hope that you enjoy using the `dev-server`, and feedback is more than welcome!