[share] README update (#2297)

Adds a little more info on how to use the plugin. Also adds linter
options to prevent any undocumented APIs from being added in the future.
diff --git a/packages/share/CHANGELOG.md b/packages/share/CHANGELOG.md
index 877cafe..f10814a 100644
--- a/packages/share/CHANGELOG.md
+++ b/packages/share/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.6.3+3
+
+* README update.
+
 ## 0.6.3+2
 
 * Remove AndroidX warnings.
diff --git a/packages/share/README.md b/packages/share/README.md
index 4536c58..3a3aa06 100644
--- a/packages/share/README.md
+++ b/packages/share/README.md
@@ -9,16 +9,26 @@
 on iOS.
 
 ## Usage
+
 To use this plugin, add `share` as a [dependency in your pubspec.yaml file](https://flutter.io/platform-plugins/).
 
 ## Example
 
-Import the library via
+Import the library.
+
 ``` dart
 import 'package:share/share.dart';
 ```
 
-Then invoke the static `share` method anywhere in your Dart code
+Then invoke the static `share` method anywhere in your Dart code.
+
 ``` dart
 Share.share('check out my website https://example.com');
 ```
+
+The `share` method also takes an optional `subject` that will be used when
+sharing to email.
+
+``` dart
+Share.share('check out my website https://example.com', subject: 'Look what I made!');
+```
diff --git a/packages/share/analysis_options.yaml b/packages/share/analysis_options.yaml
new file mode 100644
index 0000000..4d3c53a
--- /dev/null
+++ b/packages/share/analysis_options.yaml
@@ -0,0 +1,11 @@
+# This exists to add a lint for missing API docs just on this specific package,
+# since not all packages have coverage for all their public members yet and
+# adding it in would be non-trivial. `public_member_api_docs` should be applied
+# to new packages going forward, and ideally the main `analysis_options.yaml`
+# file as soon as possible.
+
+include: ../../analysis_options.yaml
+
+linter:
+  rules:
+    - public_member_api_docs
diff --git a/packages/share/example/lib/main.dart b/packages/share/example/lib/main.dart
index 1eb04e0..b68195c 100644
--- a/packages/share/example/lib/main.dart
+++ b/packages/share/example/lib/main.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// ignore_for_file: public_member_api_docs
+
 import 'package:flutter/material.dart';
 import 'package:share/share.dart';
 
diff --git a/packages/share/pubspec.yaml b/packages/share/pubspec.yaml
index de376e8..0748bd2 100644
--- a/packages/share/pubspec.yaml
+++ b/packages/share/pubspec.yaml
@@ -3,7 +3,7 @@
   the ACTION_SEND intent on Android and UIActivityViewController on iOS.
 author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/share
-version: 0.6.3+2
+version: 0.6.3+3
 
 flutter:
   plugin: