Update v0.14 schema docs and add code design doc

docs/CODE-LAYOUT.md

@@ -0,0 +1,138 @@
+# Contributing to platyPS
+
+## Get the code
+
+```
+git clone https://github.com/PowerShell/platyPS
+```
+
+## Understand code layout
+
+There are two parts:
+
+- `Markdown.MAML.dll`, a .NET library written in C#. It does the heavy lifting, like parsing
+  Markdown, transforming it into XML, and so on. You can open `.\Markdown.MAML.sln` in Visual Studio
+  on any platform.
+- A PowerShell module in `.\src\platyPS`. This module provides the user CLI.
+
+## Build
+
+To build the whole project, use the `build.ps1` helper script. It depends on the [dotnet cli][01]
+build tool.
+
+On Windows you would also need to [install full dotnet framework][02] if it's not installed already.
+
+```powershell
+.\build.ps1
+```
+
+As part of the build, platyPS generates help for itself. The output of the build is placed in
+`out\Microsoft.PowerShell.PlatyPS`.
+
+`build.ps1` also imports the module from `out\platyPS` and generates help itself.
+
+> [!NOTE]
+> If you changed C# code, `build.ps1` will try to overwrite a DLL in use. You will then need to
+> re-open your PowerShell session. If you know a better workflow, please suggest it in the Issues.
+
+## Tests
+
+Each part of the project has a test set:
+
+- The C# part has xUnit tests. You can run them from Visual Studio or from command line with
+  `dotnet test ./test/Markdown.MAML.Test`.
+- The PowerShell part has [Pester][03] tests. You can run them with `Invoke-Pester`.
+
+> [!NOTE]
+> Pester tests always force-import the module from the output ___location of `.\build.ps1`.
+
+## Schema
+
+If you have ideas or concerns about the Markdown schema, feel free to open a GitHub Issue to discuss
+it.
+
+## Repo structure
+
+- **src\platyPS** - sources to create the final PowerShell module.
+- **src\Markdown.MAML, Markdown.MAML.sln** - source code for C# Markdown to MAML converter.
+- **[platyPS.schema.md][04]** - description of Markdown that platyPS expects.
+
+## Data transformations
+
+Data transformations are the core of platyPS. A user has content in some form and she wants to
+transform it into another form. E.g. transform existing module help (in MAML) to Markdown and use it
+in the future to generate the external help (MAML) and static HTML for online references.
+
+platyPS provides APIs in the form of cmdlets for end-user scenarios. These scenarios are assembled
+from simple transformations. This chart describes these simple transformations:
+
+```
+ +----------+
+ |          |
+ |   HTML   |
+ |          |
+ +------^---+
+        |
+ +------+------------+           +-----------------+
+ |                   |           |  Markdown Model |
+ |  Markdown file    +----------->                 |
+ |                   |           +-+---------------+
+ |                   |             |
+ +---------------^---+             |
+                 |                 |
+                 |                 |
+                 |                 |
+              +--+-----------------v--+
+              |      MAML Model       |
+              | (= Generic Help model)|
+              |                       |
+              +--+-------------------^+
+                 |                   |
+                 |                   |
+                 |                   |
++----------------v-----+            ++--------------------------+
+|  MAML XML file       |            | Help Object in PowerShell |
+| (External help file) +------------> (+ Get-Command object)    |
++----------------------+            +---------------------------+
+```
+
+### Example `New-MarkdownHelp`
+
+A user creates a platyPS Markdown for the first time with `New-MarkdownHelp`:
+
+```powershell
+New-MarkdownHelp -Command New-MyCommandHelp
+```
+
+Under the hood, the following tranformations happen:
+
+```
+[MAML XML file] --> [Help Object + Get-Command object] --> [MAML Model] --> [Markdown file]
+```
+
+# Making a new release
+
+1. Make sure that `CHANGELOG.md` is up-to-date, move section from `UNRELEASED` to new section
+   `<release name>`.
+1. Make sure platyPS help itself (content in .\docs folder) is up to date.
+   `Update-MarkdownHelp -Path .\docs` should result in no changes.
+1. Do not change the version in platyps.psd1. Git tag will update this version for release.
+1. From master, tag the release.
+1. Push tag to GitHub.
+1. Find the corresponding build on AppVeyor.
+1. Download ZIP archive with the module from Appveyor's Artifacts tab.
+1. Unblock the ZIP archive (`Unblock-File foo.zip`), and copy the ZIP's contents to
+   `$env:PSMODULEPATH` so it's available to `Publish-Module`.
+1. Publish the module to the Gallery:
+   `Publish-Module -RequiredVersion <version> -Verbose -NuGetApiKey $apiKey`.
+1. Check that https://www.powershellgallery.com/packages/platyPS/ updated.
+1. Publish a new github release from https://github.com/PowerShell/platyPS/releases to move "Latest
+   release" label to the new tag.
+
+Congratulations! You just made a release.
+
+<!-- link references -->
+[01]: https://docs.microsoft.com/en-us/dotnet/core/tools/
+[02]: https://docs.microsoft.com/en-us/dotnet/framework/install/guide-for-developers
+[03]: https://github.com/pester/Pester
+[04]: platyPS.schema.md