Change to out-of source build, Update build instructions (#3271)

* update build instructions

Usage of "modern" CMake syntax and using specific out of source build.
Further add example on how to build in parallel, build a specific target
and how to change the compiler.

This closes #3236.

doc/devel/contrib/development.md

@@ -16,26 +16,46 @@ See the [TaskChampion CONTRIBUTING guide](../../../taskchampion/CONTRIBUTING.md)
  * Rust 1.64.0 or higher (hint: use https://rustup.rs/ instead of using your system's package manager)
 
 ## Obtain and Build Code:
-```
-    $ git clone --recursive https://github.com/GothenburgBitFactory/taskwarrior taskwarrior.git
-    $ cd taskwarrior.git
-    $ git checkout develop               # Latest dev branch
-    $ git submodule init                 # This is now done by cmake as a test
-    $ git submodule update               # Update the libhsared.git submodule
-    $ cmake -DCMAKE_BUILD_TYPE=debug .   # debug or release. Default: neither
-    $ make VERBOSE=1 -j4                 # Shows details, builds using 4 jobs
-                                         # Alternately 'export MAKEFLAGS=-j 4'
-```
+The following documentation works with CMake 3.14 and later.
+Here are the minimal steps to get started, using an out of source build directory and calling the underlying build tool over the CMake interface.
+See the general CMake man pages or the [cmake-documentation](https://cmake.org/cmake/help/latest/manual/cmake.1.html) for more,
 
-This will build several executables, but the one you want is probably `src/task`.
+## Basic Building
+```sh
+git clone https://github.com/GothenburgBitFactory/taskwarrior
+cd taskwarrior
+cmake -S . -B build  -DCMAKE_BUILD_TYPE=RelWithDebInfo
+cmake --build build
+```
+Other possible build types can be `Release` and `Debug`.
+This will build several executables, but the one you want is probably `src/task`, located in the `build` directory.
 When you make changes, just run the last line again.
 
-## Run the Test Suite:
+### Building a specific target
+For **only** building the `task` executable, use
+```sh
+cmake --build build --target task_executable
+```
 
+### Building in parallel
+If a parallel build is wanted use
+```sh
+cmake --build build -j <number-of-jobs>
+```
+
+### Building with clang as compiler
+```sh
+cmake -S . -B build-clang\
+    -DCMAKE_C_COMPILER=clang\
+    -DCMAKE_CXX_COMPILER=clang++
+cmake --build build-clang
+```
+
+## Run the Test Suite:
 First switch to the test directory:
 
 ```
-    $ cd test
+    $ cd build/test
 ```
 Then you can run all tests, showing details, with
 ```