add a Facebook url to About section

app/src/main/java/com/simplemobiletools/calculator/activities/AboutActivity.java

@@ -2,6 +2,7 @@ package com.simplemobiletools.calculator.activities;
 
 import android.content.Intent;
 import android.content.res.Resources;
+import android.net.Uri;
 import android.os.Bundle;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.appcompat.BuildConfig;
@@ -60,4 +61,15 @@ public class AboutActivity extends AppCompatActivity {
         final Intent intent = new Intent(getApplicationContext(), LicenseActivity.class);
         startActivity(intent);
     }
+
+    @OnClick(R.id.about_facebook)
+    public void facebookClicked() {
+        String link = "https://www.facebook.com/simplemobiletools";
+        try {
+            getPackageManager().getPackageInfo("com.facebook.katana", 0);
+            link = "fb://page/150270895341774";
+        } catch (Exception ignored) {
+        }
+        startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse(link)));
+    }
 }

app/src/main/res/layout/activity_about.xml

@@ -33,11 +33,28 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_below="@+id/about_email"
+        android:layout_marginTop="@dimen/activity_margin"
         android:paddingBottom="@dimen/activity_margin"
         android:paddingTop="@dimen/activity_margin"
         android:text="@string/third_party_licences_underlined"
         android:textColor="@color/colorPrimary"/>
 
+    <TextView
+        android:id="@+id/about_follow_us"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_below="@+id/about_license"
+        android:paddingBottom="@dimen/social_padding"
+        android:paddingTop="@dimen/activity_margin"
+        android:text="@string/follow_us"/>
+
+    <ImageView
+        android:id="@+id/about_facebook"
+        android:layout_width="@dimen/social_logo"
+        android:layout_height="@dimen/social_logo"
+        android:layout_below="@+id/about_follow_us"
+        android:src="@mipmap/facebook"/>
+
     <TextView
         android:id="@+id/about_version"
         android:layout_width="match_parent"

app/src/main/res/values/dimens.xml

@@ -6,4 +6,6 @@
     <dimen name="button_text_size">28sp</dimen>
     <dimen name="formula_text_size">20sp</dimen>
     <dimen name="display_text_size">40sp</dimen>
+    <dimen name="social_padding">8dp</dimen>
+    <dimen name="social_logo">40dp</dimen>
 </resources>

app/src/main/res/values/strings.xml

@@ -4,10 +4,11 @@
 
     <!-- About -->
     <string name="about">About</string>
-    <string name="website">For more simple apps or source codes please visit:\nhttp://simplemobiletools.com</string>
-    <string name="email_label">You can send your feedback or new app suggestions at:</string>
+    <string name="website">More simple apps and source code at:\nhttp://simplemobiletools.com</string>
+    <string name="email_label">Send your feedback or suggestions at:</string>
     <string name="email">hello@simplemobiletools.com</string>
     <string name="third_party_licences_underlined"><u>Third party licences</u></string>
+    <string name="follow_us">Follow us at:</string>
     <string name="version">v %1$s</string>
     <string name="copyright">Copyright © Simple Mobile Tools %1$d</string>