Add documentation for temci init

doc/temci_init.rst

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+temci init
+==========
+
+Commands to create documented sample config files. Accepts the option ``--settings FILE`` to configure a backing
+settings file.
+
+temci init settings
+    Creates a sample settings file with all the default (and currently applied) settings. Might be used to
+    update a settings file for a new version of temci.
+temci init build_config
+    Creates a sample build configuration file, for more information on the format see `temci build <temci_build.html#file-format>`_.
+temci init run_config
+    Creates a sample exec configuration, for more information on the format see `temci exec <temci_exec.html#file-format>`_