[web] Install cmake via pip to get a more recent version.

On Ubuntu 18.04 the systems cmake package is at version 3.10 which
is too old.

web/content/docs/devguide/getting-started/prerequisites.pandoc

@@ -174,58 +174,60 @@ If you do not have rights to install a system package (e.g. on cluster systems)
 :::
 
 
-## Step: Install CMake
+## Step: Install Python 3
 
 ::: {.win}
-- Download the installer, at the [CMake download page](http://www.cmake.org/cmake/resources/software.html) choose the **Windows (Win32 Installer)**.
-- Execute the installer, please check the **Add CMake to the system path for all users**-option
+
+- [Download the Python 3 installer](https://www.python.org/ftp/python/3.7.2/python-3.7.2-amd64-webinstall.exe)
+- Install with the following options
+  - Check *Add Python 3.X to PATH*
+  - *Customize installation*
+  - Make sure to have `pip` enabled (you may uncheck *Documentation*, *tcl/tk*, *Python test suite*)
+  - You may check *Install for all users*
+  - Check *Add Python to environment variables*!
+
 :::
 
 ::: {.linux}
-Install CMake with your favourite package manager (the two graphical user interfaces are optional):
+
+Install Python 3 and pip:
 
 ```bash
-$ sudo apt-get install cmake cmake-qt-gui cmake-curses-gui
+sudo apt-get install python3 python3-pip
 ```
+
 :::
 
 ::: {.mac}
-Install CMake with Homebrew:
+Install Python 3 with Homebrew:
 
 ```bash
-$ brew install cmake
+brew install python
 ```
 :::
 
-## Step: Install Python 3
+## Step: Install CMake
 
 ::: {.win}
-
-- [Download the Python 3 installer](https://www.python.org/ftp/python/3.7.2/python-3.7.2-amd64-webinstall.exe)
-- Install with the following options
-  - Check *Add Python 3.X to PATH*
-  - *Customize installation*
-  - Make sure to have `pip` enabled (you may uncheck *Documentation*, *tcl/tk*, *Python test suite*)
-  - You may check *Install for all users*
-  - Check *Add Python to environment variables*!
-
+- Download the installer, at the [CMake download page](http://www.cmake.org/cmake/resources/software.html) choose the **Windows (Win32 Installer)**.
+- Execute the installer, please check the **Add CMake to the system path for all users**-option
 :::
 
 ::: {.linux}
-
-Install Python 3 and pip:
+Install CMake with Pythons package manager `pip` (you may get a more recent version than using your systems package manager):
 
 ```bash
-sudo apt-get install python3 python3-pip
+$ pip3 install --user cmake
 ```
 
+This installed `cmake` and `ccmake` to `.local/bin` in your home directory. Make sure to have this directory in your `PATH`!
 :::
 
 ::: {.mac}
-Install Python 3 with Homebrew:
+Install CMake with Homebrew:
 
 ```bash
-brew install python
+$ brew install cmake
 ```
 :::