Update README for Qt6

Fixes: QTBUG-89912
Change-Id: I9e96d57d0de8eb3c10fdfa762a009e30aab93e87
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

README

@@ -1,4 +1,4 @@
-HOW TO BUILD QT5
+HOW TO BUILD Qt6
 ================
 
 
@@ -8,92 +8,79 @@ HOW TO BUILD QT5
    System requirements
    ------------------
 
+    - CMake 3.18 or later
     - Perl 5.8 or later
     - Python 2.7 or later
-    - C++ compiler supporting the C++11 standard
+    - C++ compiler supporting the C++17 standard
+
+     It's recommended to have ninja 1.8 or later installed.
 
      For other platform specific requirements,
      please see section "Setting up your machine" on:
      http://wiki.qt.io/Get_The_Source
 
-   Licensing:
-   ----------
-
-    Opensource users:
-
-        <license>        = -opensource
-
-    Commercial users:
-
-        <license>        = -commercial
-
    Linux, Mac:
    -----------
 
      cd <path>/<source_package>
-     ./configure -prefix $PWD/qtbase <license> -nomake tests
-     make -j 4
+     ./configure -prefix $PWD/qtbase
+     cmake --build .
 
    Windows:
    --------
 
      Open a command prompt.
      Ensure that the following tools can be found in the path:
-     * Supported compiler (Visual Studio 2012 or later,
-        MinGW-builds gcc 4.9 or later)
+     * Supported compiler (Visual Studio 2019 or later,
+       MinGW-builds gcc 8.1 or later)
      * Perl version 5.12 or later   [http://www.activestate.com/activeperl/]
      * Python version 2.7 or later  [http://www.activestate.com/activepython/]
      * Ruby version 1.9.3 or later  [http://rubyinstaller.org/]
 
      cd <path>\<source_package>
-     configure -prefix %CD%\qtbase <license> -nomake tests
-     nmake // jom // mingw32-make
-
-     To accelerate the bootstrap of qmake with MSVC, it may be useful to pass
-     "-make-tool jom" on the configure command line. If you do not use jom,
-     adding "/MP" to the CL environment variable is a good idea.
+     configure -prefix %CD%\qtbase
+     cmake --build .
 
  More details follow.
 
  Build!
  ======
 
- A typical `configure; make' build process is used.
+ Qt is built with CMake, and a typical
+ `configure && cmake --build .' build process is used.
+
+ If ninja is installed, it is automatically chosen as CMake generator.
 
  Some relevant configure options (see configure -help):
 
  -release              Compile and link Qt with debugging turned off.
  -debug                Compile and link Qt with debugging turned on.
- -nomake tests         Disable building of tests to speed up compilation
- -nomake examples      Disable building of examples to speed up compilation
- -confirm-license      Automatically acknowledge the LGPL 2.1 license.
 
  Example for a release build:
- (adjust the `-jN' parameter as appropriate for your system)
 
-   ./configure -prefix $PWD/qtbase <license>
-   make -j4
+   ./configure -prefix $PWD/qtbase
+   cmake --build .
 
  Example for a developer build:
  (enables more autotests, builds debug version of libraries, ...)
 
-   ./configure -developer-build <license>
-   make -j4
+   ./configure -developer-build
+   cmake --build .
 
  See output of `./configure -help' for documentation on various options to
  configure.
 
- The above examples will build whatever Qt5 modules have been enabled by
- default in the build system.
+ The above examples will build whatever Qt modules have been enabled
+ by default in the build system.
 
- It is possible to build selected modules with their dependencies by doing
- a `make module-<foo>'.  For example, to build only qtdeclarative,
+ It is possible to build selected repositories with their dependencies by doing
+ a `ninja <repo-name>/all'.  For example, to build only qtdeclarative,
  and the modules it depends on:
 
-   ./configure -prefix $PWD/qtbase <license>
-   make -j4 module-qtdeclarative
+   ./configure
+   ninja qtdeclarative/all
 
- This can save a lot of time if you are only interested in a subset of Qt5.
+ This can save a lot of time if you are only interested in a subset of Qt.
 
 
  Hints
@@ -103,32 +90,28 @@ HOW TO BUILD QT5
  developers and release engineers. Consider adding qtrepotools/bin
  to your PATH environment variable to access them.
 
- The qt5_tool in qtrepotools has some more features which may be of interest.
- Try `qt5_tool --help'.
 
-
- Building Qt5 from git
+ Building Qt from git
  =====================
- See http://wiki.qt.io/Building_Qt_5_from_Git and README.git
+ See http://wiki.qt.io/Building_Qt_6_from_Git and README.git
  for more information.
- See http://wiki.qt.io/Qt_5 for the reference platforms.
+ See http://wiki.qt.io/Qt_6 for the reference platforms.
 
 
  Documentation
  =============
 
  After configuring and compiling Qt, building the documentation is possible by running
- "make docs".
+ "cmake --build . --target docs".
 
  After having built the documentation, you need to install it with the following
  command:
 
-    make install_docs
+    cmake --build . --target install_docs
 
- The documentation is installed in the path set to $QT_INSTALL_DOCS.
- Running "qmake -query" will list the value of QT_INSTALL_DOCS.
+ The documentation is installed in the path specified with the
+ configure argument -docdir.
 
- Information about Qt 5's documentation is located in qtbase/doc/README
- or in the following page: http://wiki.qt.io/Qt5DocumentationProject
+ Information about Qt's documentation is located in qtbase/doc/README
 
  Note: Building the documentation is only tested on desktop platforms.