Add documentation about generating exercise READMEs

maintaining-a-track/regenerating-exercise-readmes.md

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+# Regenerating Exercise READMEs
+
+In order to give maintainers more control over the contents and formatting of each exercise README, it is generated from a template that the maintainers control. However, in order to avoid having to reinvent the universe from scratch when porting a new exercise from a shared specification, this README can be generated based on the specification description and other metadata.
+
+## Setup
+
+Install [configlet][]. You will need version 3.0.0 or higher.
+
+If any of the exercises in your track are based on problems in the [problem-specifications][] repository, then you will
+need to have a copy of that repository locally on disk, in the same directory as your track.
+
+```
+.
+├── your-track/
+└── problem-specifications/
+```
+
+## Generating the READMEs
+
+Call the `configlet generate` command with the path to the track.
+
+If you are in the track's root directory, then call it with `.`:
+
+```
+configlet generate .
+```
+
+By default this generates all the READMEs for all the exercises. In order to generate the README for a particular exercise, pass the `--only` flag with a slug:
+
+```
+configlet generate . --only hello-world
+```
+
+## The README Template
+
+The template can be found at `$TRACK_ROOT/exercises/$SLUG/.meta/readme.go.tmpl`, and is written using Go's [text/template][text-template] package.
+
+There are a number of values available in the template:
+
+`.Spec` represents the problem specification, which is either a shared specification from [problem-specifications][], or a custom specification found in the exercise's `.meta` directory. The following values on `.Spec` can be referenced within the template:
+
+- `.Spec.Slug` - the exercise's slug
+- `.Spec.Name` - the wordified slug
+- `.Spec.Description` - the contents of the `description.md` file
+- `.Spec.Source` - a textual description of where the idea for the exercise came from (optional)
+- `.Spec.SourceURL` - a link to something about the source (optional)
+- `.Spec.Credits` - combines source and source_url into a readable bit of metadata
+
+In addition to the values on `.Spec`, there are two additional bits of text that can be included:
+
+- `.Hints` - the contents of the optional `HINTS.md` which lives in the root of the exercise directory.
+- `.TrackInsert` - the contents of the `EXERCISE_README_INSERT.md` file, which lives in the track's `docs` directory.
+
+### Default Template
+
+The default contents of `.meta/readme.go.tmpl` is:
+
+```
+# {{ .Spec.Name }}
+
+{{ .Spec.Description -}}
+{{- with .Hints }}
+{{ . }}
+{{ end }}
+{{- with .TrackInsert }}
+{{ . }}
+{{ end }}
+{{- with .Spec.Credits -}}
+## Source
+
+{{ . }}
+{{ end }}
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+```
+
+[configlet]: https://github.com/exercism/configlet
+[text-template]: https://golang.org/pkg/text/template/
+[problem-specifications]: https://github.com/exercism/problem-specifications
+