Qt/Intro: Explain a bit more what will happen first time

Author: luke-jr

src/qt/forms/intro.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>674</width>
-    <height>363</height>
+    <height>415</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -200,6 +200,36 @@
      </item>
     </layout>
    </item>
+   <item>
+    <widget class="QLabel" name="lblExplanation1">
+     <property name="text">
+      <string>When you click OK, %1 will begin to download and process the full %4 block chain (%2GB) starting with the earliest transactions in %3 when %4 initially launched.</string>
+     </property>
+     <property name="wordWrap">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <widget class="QLabel" name="lblExplanation2">
+     <property name="text">
+      <string>This initial synchronisation is very demanding, and may expose hardware problems with your computer that had previously gone unnoticed. Each time you run %1, it will continue downloading where it left off.</string>
+     </property>
+     <property name="wordWrap">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
+   <item>
+    <widget class="QLabel" name="lblExplanation3">
+     <property name="text">
+      <string>If you have chosen to limit block chain storage (pruning), the historical data must still be downloaded and processed, but will be deleted afterward to keep your disk usage low.</string>
+     </property>
+     <property name="wordWrap">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
    <item>
     <spacer name="verticalSpacer">
      <property name="orientation">

src/qt/intro.cpp

@@ -124,6 +124,15 @@ Intro::Intro(QWidget *parent) :
     ui->setupUi(this);
     ui->welcomeLabel->setText(ui->welcomeLabel->text().arg(tr(PACKAGE_NAME)));
     ui->storageLabel->setText(ui->storageLabel->text().arg(tr(PACKAGE_NAME)));
+
+    ui->lblExplanation1->setText(ui->lblExplanation1->text()
+        .arg(tr(PACKAGE_NAME))
+        .arg(BLOCK_CHAIN_SIZE)
+        .arg(2009)
+        .arg(tr("Bitcoin"))
+    );
+    ui->lblExplanation2->setText(ui->lblExplanation2->text().arg(tr(PACKAGE_NAME)));
+
     uint64_t pruneTarget = std::max<int64_t>(0, GetArg("-prune", 0));
     requiredSpace = BLOCK_CHAIN_SIZE;
     QString storageRequiresMsg = tr("At least %1 GB of data will be stored in this directory, and it will grow over time.");
@@ -133,6 +142,9 @@ Intro::Intro(QWidget *parent) :
             requiredSpace = prunedGBs;
             storageRequiresMsg = tr("Approximately %1 GB of data will be stored in this directory.");
         }
+        ui->lblExplanation3->setVisible(true);
+    } else {
+        ui->lblExplanation3->setVisible(false);
     }
     requiredSpace += CHAIN_STATE_SIZE;
     ui->sizeWarningLabel->setText(