Merge pull request #178 from olehermanse/docs

ENT-11175: Rewrote the intro to be more clear about different types of projects

JSON.md

@@ -1,14 +1,28 @@
 # CFEngine Build JSON file format
 
-The CFEngine Build website and tooling relies on JSON files for different purposes;
+The `cfbs` command line tool uses `cfbs.json` configuration files.
+We call the folder / git repo which has a `cfbs.json` file (and optionally other files and folders) a _project_, and the end result after combining modules in a project into policy a _policy set_.
+The _policy set_ is what you deploy to your CFEngine hub / policy server, in `/var/cfengine/masterfiles`.
 
-* The project file (`cfbs.json`) generated by running `cfbs init` when you start a new project
-* The index of all available modules which is available on GitHub
-* A `cfbs.json` file with necessary metadata for adding a module using URL (not from index)
+See the [README](https://github.com/cfengine/cfbs/blob/master/README.md) for general documentation on the `cfbs` tool and its commands.
+This file is specifically about the `cfbs.json` file format, it should serve as detailed and useful information for more advanced users who are making their own modules or contributing to CFEngine Build.
 
-All these 3 share 1 standard format, commonly called `cfbs.json`.
+The type of a project is specified in a top-level `type` key in `cfbs.json`.
+There are 3 types of projects:
 
-(There is also [`versions.json`](https://github.com/cfengine/cfbs-index/blob/master/versions.json), but this specification is not about that file).
+* For building a policy set you create a project with type `policy-set`.
+  This is the default when running `cfbs init`, and what most users encounter when first using the tool and CFEngine.
+  You then need to use the top-level `build` key to specify which modules to use in `cfbs build`.
+* The index of all available modules for `cfbs add <module-name>` has type `index`.
+  The available modules must be in a dictionary in the `index` field.
+  By default, [this index available GitHub](https://github.com/cfengine/build-index/blob/master/cfbs.json) is used.
+* When developing your own reusable modules to use in other projects, `module` type is used.
+
+When `cfbs` is using the default index and when we build the [build.cfengine.com](https://build.cfengine.com) website, we use a separate [`versions.json`](https://github.com/cfengine/build-index/blob/master/versions.json) file to keep track of all the versions of modules, their tarballs and checksums.
+When contributors edit the index ([like this](https://github.com/cfengine/build-index/pull/465/files)), an automated PR is generated to make the appropriate edit to `versions.json` ([like this](https://github.com/cfengine/build-index/pull/466/files)), (after downloading and uploading the module), so users don't have to update `versions.json` manually.
+
+Note that while the 3 types above add some requirements to which fields you must use, the file format and `cfbs` tool is quite flexible.
+It is for example entirely possible, and encouraged, to use the `build` field and `cfbs build` command to build and test a policy set, while you are working on a module in a project with type `module`.
 
 ## The process of building modules from a project into a policy set