[nnbd migration] move the docs for the NNBD migration tool

Change-Id: I932da23be10839b5bde6034f120763c54f63889f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/140102
Reviewed-by: Janice Collins <jcollins@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>

pkg/analysis_server/lib/src/edit/nnbd_migration/README.md

@@ -1,50 +0,0 @@
-# Null Safety Migration Tooling
-
-Note: the null safety migration tooling and workflow is in an early state;
-this doc will be updated as the steps and workflow are simplified.
-
-## Building the NNBD sdk
-
-In order to run the tool currently you have to be able to build your own copy
-of the Dart SDK.
-
-To do this, run:
-
-```
-./tools/build.py -mrelease --nnbd create_sdk
-```
-
-The NNBD sdk now lives under the ReleaseX64NNBD sub-directory of your build
-directory, e.g.
-
-```
-xcodebuild/ReleaseX64NNBD/dart-sdk/
-```
-
-## Migrating a package
-
-- build a NNBD version of the SDK (see above)
-- select a package to work on
-- in that package, edit the `analysis_options.yaml` to enable the NNBD
-  experiment from the POV of the analyzer:
-```yaml
-analyzer:
-  enable-experiment:
-    - non-nullable
-```
-- run `pub get` for the package (and, verify that the
-  `.dart_tool/package_config.json` file was created)
-
-Then, run the migration tool from the top-level of the package directory:
-
-```
-<sdk-repo>/xcodebuild/ReleaseX64NNBD/dart migrate .
-```
-
-The migration tool will run, print the proposed changes to the console, and
-display a url for the preview tool. Open that url from a browser to see a rich
-preview of the proposed null safety changes.
-
-## Using the tool
-
-TODO:

pkg/analysis_server/lib/src/edit/nnbd_migration/resources/index.html

@@ -53,7 +53,7 @@
 </div><!-- /panels -->
 <footer>
     <a target="_blank"
-       href="https://github.com/dart-lang/sdk/blob/master/pkg/analysis_server/lib/src/edit/nnbd_migration/README.md">Null
+       href="https://github.com/dart-lang/sdk/blob/master/pkg/nnbd_migration/README.md">Null
         safety migration help</a>
     <span class="wide"> </span>
     <div>Based on {{ sdkVersion }}</div>

pkg/nnbd_migration/README.md

@@ -1,4 +1,54 @@
-# NNBD Migration Engine
+# Null Safety Migration Tooling
 
-This package provides infrastructure for migrating code to be non-nullable by
-default.
+Note: the null safety migration tooling and workflow is in an early state;
+this doc will be updated as the steps and workflow are simplified.
+
+## Building the NNBD sdk
+
+In order to run the tool currently you have to be able to build your own copy
+of the Dart SDK.
+
+To do this, run:
+
+```
+./tools/build.py -mrelease --nnbd create_sdk
+```
+
+The NNBD sdk now lives under the ReleaseX64NNBD sub-directory of your build
+directory, e.g.
+
+```
+xcodebuild/ReleaseX64NNBD/dart-sdk/
+```
+
+## Trying this for Flutter devs
+
+TODO:
+
+## Migrating a package
+
+- build a NNBD version of the SDK (see above)
+- select a package to work on
+- in that package, edit the `analysis_options.yaml` to enable the NNBD
+  experiment from the POV of the analyzer:
+```yaml
+analyzer:
+  enable-experiment:
+    - non-nullable
+```
+- run `pub get` for the package (and, verify that the
+  `.dart_tool/package_config.json` file was created)
+
+Then, run the migration tool from the top-level of the package directory:
+
+```
+<sdk-repo>/xcodebuild/ReleaseX64NNBD/dart migrate .
+```
+
+The migration tool will run, print the proposed changes to the console, and
+display a url for the preview tool. Open that url from a browser to see a rich
+preview of the proposed null safety changes.
+
+## Using the tool
+
+TODO: