STYLE: add Readme.txt with instructions how to build cmake, fix #5296

Alex

Readme.txt

@@ -0,0 +1,53 @@
+This is CMake, the cross-platform, open-source make system.
+CMake is free software under a BSD-like license, see Copyright.txt .
+For documentation see the Docs/ directory once you have built CMake 
+or visit http://www.cmake.org.
+
+
+Building CMake
+==============
+
+
+Supported Platforms
+-------------------
+
+MS Windows, Mac OS X, Linux, FreeBSD, Solaris, HP-UX, IRIX, BeOS, QNX
+
+Other UNIX-like operating systems may work too out of the box, if not
+it shouldn't be a major problem to port CMake to this platform. Contact the
+CMake mailing list in this case: http://www.cmake.org/mailman/listinfo/cmake
+
+
+You don't have any previous version of CMake already installed
+--------------------------------------------------------------
+
+* UNIX/Mac OSX/MinGW/MSYS/Cygwin:
+
+You need to have a compiler and a make installed.
+Run the configure script you find the in the source directory of CMake.
+You can use the --help option to see the supported options.
+You may want to use the --prefix=<install_prefix> option to specify a custom
+installation directory for CMake. You can run the configure script from
+within the CMake source directory or any other build directory of your
+choice. Once this has finished successfully, run make and make install.
+So basically it's the same as you may be used to from autotools-based
+projects:
+$ ./configure; make; make install
+
+
+* Other Windows:
+You need to download and install a binary release of CMake in order to build CMake.
+You can get these releases from http://www.cmake.org/HTML/Download.html .
+Then proceed with the instructions below:
+
+
+You already have a version of CMake installed
+---------------------------------------------
+
+You can build CMake as any other project with a CMake-based buildsystem:
+run the installed CMake on the sources of this CMake with your prefered
+options and generators. Then build it and install it.
+For instructions how to do this, see http://www.cmake.org/HTML/RunningCMake.html 
+
+
+The CMake team