Update documentation for toolchain option dicts

Touched up documentation for the `scalafmt` and `scala_proto`
toolchains.

Author: mbland

README.md

@@ -930,19 +930,36 @@ parameter list, which is almost in complete correspondence with parameters from
 the previous macros. The `WORKSPACE` files in this repository also provide many
 examples.
 
-### Replacing toolchain registration macros in `WORKSPACE`
+### Replacing toolchain registration macros
 
 Almost all `rules_scala` toolchains configured using `scala_toolchains()` are
-automatically registered by `scala_register_toolchains()`. There are two
-toolchain macro replacements that require special handling.
+automatically registered by `scala_register_toolchains()`. The same is true for
+toolchains configured using the `scala_deps` module extension under Bzlmod.
+There are two toolchain macro replacements that require special handling.
 
 The first is replacing `scala_proto_register_enable_all_options_toolchain()`
-with the following `scala_toolchains()` parameters:
+with the following:
 
 ```py
+# MODULE.bazel
+
+scala_deps.scala_proto(
+    "default_gen_opts" = [
+        "flat_package",
+        "grpc",
+        "single_line_to_proto_string",
+    ],
+)
+
+# WORKSPACE
 scala_toolchains(
-    scala_proto = True,
-    scala_proto_options = [],
+    scala_proto = {
+        "default_gen_opts": [
+            "flat_package",
+            "grpc",
+            "single_line_to_proto_string",
+        ],
+    },
 )
 ```
 

docs/phase_scalafmt.md

@@ -75,7 +75,7 @@ The extension provides a default configuration, but there are 2 ways to use
 a custom configuration:
 
 - Put `.scalafmt.conf` at the root of your workspace
-- Pass `.scalafmt.conf` in via `scala_toolchains`:
+- Pass `.scalafmt.conf` into the toolchain configuration:
 
     ```py
     # MODULE.bazel

docs/scala_proto_library.md

@@ -1,22 +1,40 @@
 # scala_proto_library
 
-To use this rule, you'll first need to add the following to your `WORKSPACE` file,
-which adds a few dependencies needed for ScalaPB:
+To use this rule, add the following configuration, which adds the dependencies
+needed for ScalaPB:
 
 ```py
-scala_toolchains(
-    # Other toolchains settings...
-    scala_proto = True,
-    scala_proto_options = [
+# MODULE.bazel
+scala_deps.scala_proto(
+    "default_gen_opts" = [
         "grpc",
         "flat_package",
         "scala3_sources",
     ],
 )
+```
+
+```py
+# WORKSPACE
+scala_toolchains(
+    # Other toolchains settings...
+    scala_proto = {
+        "default_gen_opts": [
+            "grpc",
+            "flat_package",
+            "scala3_sources",
+        ],
+    },
+)
 
 scala_register_toolchains()
 ```
 
+See the __scalapbc__ column of the [__ScalaPB: SBT Settings > Additional options
+to the generator__](
+https://scalapb.github.io/docs/sbt-settings#additional-options-to-the-generator
+) table for `default_gen_opts` values.
+
 Then you can import `scala_proto_library` in any `BUILD` file like this:
 
 ```py

scala_proto/toolchains.bzl

@@ -16,6 +16,10 @@ def setup_scala_proto_toolchains(
     See //scala/private:macros/toolchains_repo.bzl for details, especially the
     _SCALA_PROTO_TOOLCHAIN_BUILD string template.
 
+    See the `scalapbc` column of the "ScalaPB: SBT Settings > Additional options
+    to the generator" table below for `default_gen_opts` values:
+    - https://scalapb.github.io/docs/sbt-settings#additional-options-to-the-generator
+
     Args:
       name: prefix for all generate toolchains
       default_gen_opts: parameters passed to the default generator