Create a branch roadmap (#1571)

* Create a branch roadmap

This should show the general layout of how we're using branches to produce prospective text for upcoming versions.

* fix branch name

I mistyped the branch name when creating it, but there it is.

Author: BillWagner

admin/branch-diagram.md

@@ -0,0 +1,97 @@
+# Version and Feature branch diagram
+
+We've started building branches that have preliminary text for the C# language features in versions greater than the current standard. This gives the committee a look forward to how other features could be integrated into the standard. We also hope it enables us to move more quickly by having drafts ready for all future versions.
+
+A downside is that we have more complicated branch management to ensure changes we make in the standard at version 8 are propagated forward through all the branches for each upcoming version.
+
+The following diagram shows the primary branches we're using in this process.  Our naming conventions are as follows:
+
+- Branches that have the prefix *standard* represent the approved ECMA standard for the stated version.
+- Branches that have the *draft* represent the current working draft for the stated version. Updates in the *draft* branches have been approved by the committee. However, feature language may be incomplete. Issues for the draft are generally tracked with issues.
+- Branches that have the *alpha* suffix represent a "feature complete" version of the standard. However, the language for any features not incorporated in the standard hasn't been discussed by the committee.
+
+Note that all alpha versions beyond the next version (version 9) are built on the previous version's alpha branch. Therefore the unreviewed language in the *alpha* branches accumulates with each version ahead of the committee.
+
+```mermaid
+---
+title: C# Standard - Version and Feature Branches
+---
+gitGraph
+   commit id: "standard-v5"
+   commit id: "standard-v6"
+   branch standard-v7
+   checkout standard-v7
+   commit id: "v7 features"
+   branch draft-v8
+   checkout draft-v8
+   commit id: "v8 features"
+   branch draft-v9
+   checkout draft-v9
+   commit id: "v9 base"
+   commit id: "v9 reviewed features"
+   branch v9-alpha
+   commit id: "v9 alpha feature PRs"
+   branch draft-10
+   checkout draft-10
+   commit id: "v10 base"
+   commit id: "v10 reviewed features"
+   branch v10-alpha
+   commit id: "v10 alpha feature PRs"
+   branch draft-v11
+   checkout draft-v11
+   commit id: "v11 base"
+   commit id: "v11 reviewed features"
+   branch v11-alpha
+   commit id: "v11 alpha feature PRs"
+```
+
+After each meeting, all changes merged since the previous meeting are propagated through each of the version specific branches. The following diagram shows the workflow:
+
+```mermaid
+---
+title: C# Standard - Version and Feature Branches
+---
+gitGraph
+   commit id: "standard-v5"
+   commit id: "standard-v6"
+   branch standard-v7
+   checkout standard-v7
+   commit id: "v7 features"
+   branch draft-v8
+   checkout draft-v8
+   commit id: "v8 features"
+   branch draft-v9
+   checkout draft-v9
+   commit id: "v9 base"
+   commit id: "v9 reviewed features"
+   branch v9-alpha
+   commit id: "v9 alpha feature PRs"
+   branch draft-10
+   checkout draft-10
+   commit id: "v10 base"
+   commit id: "v10 reviewed features"
+   branch v10-alpha
+   commit id: "v10 alpha feature PRs"
+   branch draft-v11
+   checkout draft-v11
+   commit id: "v11 base"
+   commit id: "v11 reviewed features"
+   branch v11-alpha
+   commit id: "v11 alpha feature PRs"
+   checkout draft-v8
+   commit id: "PRs merged at meeting"
+   checkout draft-v9
+   merge draft-v8
+   checkout v9-alpha
+   merge draft-v9
+   checkout draft-10
+   merge v9-alpha
+   checkout v10-alpha
+   merge draft-10
+   checkout draft-v11
+   merge v10-alpha
+   checkout v11-alpha
+   merge draft-v11
+```
+
+The changes approved by the committee are propagated in turn through all *draft* and *alpha* branches for upcoming versions. This process will introduce conflicts in feature specific PRs that will be resolved after the above workflow is completed.