LIB-17: Add readme (#5)

* add readme

* fix some formatting

* more formatting

* more language fixes

* add license.txt

Author: stephenruda

LICENSE.txt

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+The MIT License (MIT)
+
+Copyright (c) 2020 Simply Made Apps
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# PreferenceHelper
+A more painless way to set/get with SharedPreferences.
+# Getting Started
+Add it in your root build.gradle at the end of repositories:
+```groovy
+allprojects {
+    repositories {
+        maven { url 'https://jitpack.io' }
+    }
+}
+```
+Add the following to the dependencies section of app/build.gradle (check Releases for the latest version):
+```
+implementation 'com.github.simplymadeapps:PreferenceHelper:1.1.1'
+```
+
+# Usage
+Init the library in the `Application.onCreate()` method.  You can also put this at that top of your start activity's `onCreate()`.  All that matters is `init()` is called before any other calls to the PreferenceHelper.
+```java
+public class MyApplication extends Application {
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        PreferenceHelper.init(this);
+    }
+}
+```
+Now that the library has been initialized, you can easily use `put()` and `get()`.
+
+Storing an object:
+```
+PreferenceHelper.put("current_user_name", "John Doe");
+```
+
+Getting an object:
+```
+String username = PreferenceHelper.get("current_user_name", "No Name");
+```
+
+The library is using the object type of the input or fallback to determine what SharedPreference method to use (ex, putString, putLong, putInt, etc).
+This can cause confusion when you pass in a null object as one of these parameters.  If you need to store a null object or retrieve an object with a null fallback you should pass in that object type.
+
+Storing a null string:
+```
+PreferenceHelper.put("current_user_name", null, String.class);
+```
+
+Getting a set with a null fallback:
+```
+Set<String> usernames = PreferenceHelper.get("all_names", null, Set.class);
+```
+Note that primitive types (int, boolean, float, long) cannot be null.
+
+
+You can also check if a value has been stored with: 
+```
+boolean key_exists = PreferenceHelper.contains("some_key");
+```
+
+The library can only store what the default SharedPreferences stores (String, int, boolean, float, long, Set<String>).  It currently does not support storing of a custom objects.  This may be expanded upon in the future.
+
+# Contributing
+1. Fork it
+2. Create your feature branch (`git checkout -b my-new-feature`)
+3. Commit your changes (`git commit -am 'Add some feature'`)
+4. Push to the branch (`git push origin my-new-feature`)
+5. Create new Pull Request
+
+# License
+The library is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).