[fxicfg] Add some docs
Bug: IN-1102 #comment
Change-Id: I1e9597a61224f66c1f87b9e25cf8d970ec16a81f
diff --git a/cmd/fxicfg/CONTRIBUTING.md b/cmd/fxicfg/CONTRIBUTING.md
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+# Contributing
+
+## Source code
+
+Most of the code lives in //infra/infra/fxicfg. The directories are:
+
+* `builtins/`: starlark callables that are globally available (no `load`statement needed)
+* `errs/`: internal error handling utilities.
+* `loaders/`: packages the interpreter uses to load starlark modules.
+* `starlark/`: built-in or generated starlark code. Starlark sources in this directory are
+compiled into this binary.
+* `state/`: interpreter state, which tracks output generated by client programs.
+
+
+## Steps to add or update recipe protobuf APIs.
+
+Whenever a new protobuf API is created for a recipe, or an existing API is updated, the
+new .proto file should be added to this tool by following the steps below. These should
+be done in the //infra/infra/fxcicfg directory:
+
+1. Put the .proto file in starlark/protos/recipes
+2. Update starlark/protos/gen.go with a line to generate Go for the .proto file
+3. Run `go generate ./...`
+4. Update loaders/protos.go with a line to allow importing the generated protobuf lib.
+
+Make sure the proto definition has the following header, replacing 'fuchsia' with the
+appropriate string:
+
+```proto
+syntax = "proto3";
+
+// "from PB.recipe_modules.infra.fuchsia import Fuchsia" (from recipes)
+package recipe_modules.infra.fuchsia;
+
+option go_package = "recipes";
+```
diff --git a/cmd/fxicfg/README.md b/cmd/fxicfg/README.md
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+# fxicfg
+
+Fxicfg is a starlark interpreter for generating textproto inputs to Fuchsia
+recipes. This tool is temporary, it should eventually be superceded by LUCI's
+[lucicfg].
+
+## Usage
+
+```
+go install fuchsia.googlesource.com/infra/infra/cmd/fxicfg
+fxicfg help
+```
+
+To generate protos, be sure to run this in the same directory as `main.star`.
+
+```
+fxicfg generate main.star
+```
+
+By default, this writes files into a "generated" directory. Any files in `generated` that
+weren't generated by main.star are removed.
+
+See the configuration files in [fuchsia.git] for example starlark.
+
+[fuchsia.git]: https://fuchsia.googlesource.com/fuchsia/+/master/infra/config
+[lucicfg]: https://cs.chromium.org/chromium/infra/go/src/go.chromium.org/luci/lucicfg/cmd/lucicfg/?q=lucicfg&sq=package:chromium&dr
