Doc/Extending: Update "getting and building" page

qmake files were still referenced.
Do not focus on building Qt Creator, we ship a development package
nowadays which is preferred.

Change-Id: If209f48c0fcf4f8fbe87ecaddae826ad3a63c209
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

doc/qtcreatordev/src/creating-plugins.qdoc

@@ -31,7 +31,7 @@
     \section1 Basics
 
     \list
-        \li \l{Getting and Building Qt Creator}
+        \li \l{Getting Qt and Qt Creator}
         \li \l{Creating Your First Plugin}
         \li \l{Plugin Meta Data}
         \li \l{Plugin Life Cycle}

doc/qtcreatordev/src/getting-and-building.qdoc

@@ -3,53 +3,67 @@
 
 /*!
     \page getting-and-building.html
-    \title Getting and Building Qt Creator
+    \title Getting Qt and Qt Creator
 
-    \code
+    To create and build a \QC plugin, you need a compatible version of Qt,
-    TODO: This should be extended.
+    and either a \QC package (released or snapshot) or your own \QC build.
-    * Windows specific hassle, see README in \QC sources
-    \endcode
 
     There are several reasons why you might want to do your own build of \QC,
     like using the most current development version and being able to tweak \QC
-    at one or the other place. It is also necessary if you want to create your
+    at one or the other place. But it is not strictly necessary for creating
-    own \QC plugin.
+    plugins. The \QC packages contain a \uicontrol {Plugin Development}
+    component that enables plugin development with the \QC contained in the
+    package.
 
     \section1 Getting Qt
 
-    Prebuilt \QC packages usually use the latest stable release of Qt. You can
+    Prebuilt \QC packages usually use the latest stable release of Qt.
-    see the exact minimum requirement at the top of \QC's \c {qtcreator.pro}.
+    See the exact Qt version that a \QC package was built with in its
-    (You can find the current version in our source repository here:
+    \uicontrol {About \QC} dialog.
-    \l{https://code.qt.io/cgit/qt-creator/qt-creator.git/tree/qtcreator.pro#n4}.)
+
+    The minimum requirement for building \QC is stated in the
+    \l{https://code.qt.io/cgit/qt-creator/qt-creator.git/about/README.md}
+    {README.md} and near the top of the
+    \l{https://code.qt.io/cgit/qt-creator/qt-creator.git/tree/cmake/QtCreatorAPI.cmake}
+    {cmake/QtCreatorAPI.cmake} file in the sources.
 
     You can get prebuilt Qt packages from
     \l{https://download.qt.io}{Qt Downloads}. If you want to use Qt as provided
     by your Linux distribution, you need to make sure that all Qt development
     packages and private header packages are also installed.
 
-    \section1 Getting and Building \QC
+    \section1 Getting \QC
+
+    \section2 Installing a Prebuilt Package
+
+    The prebuilt \QC packages contain a \uicontrol {Plugin Development}
+    component that contains the CMake files, headers and other files
+    that you need to build a plugin. It is not installed by default, so make
+    sure to select the component when installing \QC.
+
+    When developing your plugin, point the \c {CMAKE_PREFIX_PATH} to the
+    installation location of \QC, or the \QC app on macOS.
+
+    Get prebuilt packages either from the
+    \l{https://download.qt.io/official_releases/online_installers/}
+    {Qt online installer}, or a standalone \QC installer either for a
+    \l{https://download.qt.io/official_releases/qtcreator/}
+    {released \QC version} or a \l{https://download.qt.io/snapshots/qtcreator/}
+    {development snapshot}.
+
+    \section2 Building \QC
 
     You can get the \QC sources for a specific version either by using one of
-    the released source bundles, or from the Git repository
+    the released source bundles or by cloning the sources from the Git repository
     \l{https://code.qt.io/cgit/qt-creator/qt-creator.git}. If you intend to
     contribute to \QC itself, you should use the repository from our Gerrit
     review tool as described in:
     \l{https://wiki.qt.io/Setting_up_Gerrit}{Setting up Gerrit}.
 
-    We strongly encourage you to do out-of-source builds of \QC (also called
+    Refer to the
-    shadow-builds).
+    \l{https://code.qt.io/cgit/qt-creator/qt-creator.git/about/README.md}
+    {README.md} included in the sources for details on building \QC.
 
-    After you put the \QC sources somewhere (lets call the path
+    When developing your plugin, point the \c {CMAKE_PREFIX_PATH} to the
-    \c {<QtCreatorSources>})
+    build location of \QC.
-    you build it on Linux and Mac with
-
-    \code
-    cd <QtCreatorSources>/..
-    mkdir qtcreator-build
-    cd qtcreator-build
-    <QtInstall>/bin/qmake -r <QtCreatorSources>
-    make
-    \endcode
-
-    or the corresponding commands on Windows systems.
 */