ui: Update completions on docset add (fixes #478)

Update completions in search box whenever a docset is installed or
removed.

src/ui/mainwindow.cpp

@@ -230,6 +230,7 @@ MainWindow::MainWindow(Core::Application *app, QWidget *parent) :
 
     connect(m_application->docsetRegistry(), &DocsetRegistry::docsetRemoved,
             this, [this](const QString &name) {
+        setupSearchBoxCompletions();
         for (SearchState *searchState : m_tabs) {
 #ifdef USE_WEBENGINE
             if (docsetName(searchState->page->url()) != name)
@@ -246,6 +247,11 @@ MainWindow::MainWindow(Core::Application *app, QWidget *parent) :
         }
     });
 
+    connect(m_application->docsetRegistry(), &DocsetRegistry::docsetAdded,
+            this, [this](const QString &) {
+        setupSearchBoxCompletions();
+    });
+
     connect(ui->lineEdit, &QLineEdit::textChanged, [this](const QString &text) {
         if (!m_searchState || text == m_searchState->searchQuery)
             return;