about: add missing elements

This commit adds two missing elements on the about screen:
- a short description of Ring
- the authors and artists list

Change-Id: Id141bfa77378449b08d165a7b32688fe34f45f19
Reviewed-by: Hadrien De Sousa <hadrien.desousa@savoirfairelinux.com>
Tuleap: #1574
diff --git a/ring-android/app/src/main/res/layout/frag_about.xml b/ring-android/app/src/main/res/layout/frag_about.xml
index b750046..5f8582a 100644
--- a/ring-android/app/src/main/res/layout/frag_about.xml
+++ b/ring-android/app/src/main/res/layout/frag_about.xml
@@ -21,7 +21,7 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent">
 
-    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:orientation="vertical"
@@ -37,6 +37,14 @@
             android:maxWidth="250dp"
             android:scaleType="fitCenter" />
 
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginBottom="16dp"
+            android:layout_marginTop="16dp"
+            android:text="@string/description"
+            android:textAlignment="center" />
+
         <LinearLayout
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
@@ -68,9 +76,9 @@
             android:id="@+id/contribute_container"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
+            android:layout_margin="5dp"
             android:background="?attr/selectableItemBackground"
             android:clickable="true"
-            android:layout_margin="5dp"
             android:gravity="center_vertical"
             android:orientation="vertical">
 
@@ -125,9 +133,9 @@
             android:id="@+id/license_container"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
+            android:layout_margin="5dp"
             android:background="?attr/selectableItemBackground"
             android:clickable="true"
-            android:layout_margin="5dp"
             android:gravity="center_vertical"
             android:orientation="vertical">
 
@@ -173,7 +181,7 @@
                 android:id="@+id/email_report"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
-                android:clickable="false"/>
+                android:clickable="false" />
 
         </LinearLayout>
 
@@ -209,5 +217,17 @@
 
         </LinearLayout>
 
+        <android.support.v7.widget.AppCompatButton
+            android:id="@+id/credits"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_gravity="center_horizontal"
+            android:paddingLeft="24dp"
+            android:paddingRight="24dp"
+            android:text="@string/credits"
+            android:theme="@style/ButtonColoredInverse" />
+
     </LinearLayout>
 </ScrollView>
+
+