Add tt init reference page (#3330)

Resolves #3323

Author: p7nov

doc/reference/tooling/tt_cli/commands.rst

@@ -30,6 +30,8 @@ help for the given command.
             -   Create an application from a template
         *   -   :doc:`help <help>`
             -   Display help for ``tt`` or a specific command
+        *   -   :doc:`init <init>`
+            -   Create a new ``tt`` environment in the current directory
         *   -   :doc:`logrotate <logrotate>`
             -   Rotate instance logs
         *   -   :doc:`play <play>`

doc/reference/tooling/tt_cli/init.rst

@@ -0,0 +1,52 @@
+.. _tt-init:
+
+Creating a tt environment
+=========================
+
+..  code-block:: bash
+
+    tt init
+
+``tt init`` creates a ``tt`` environment in the current directory. This includes:
+
+*   Setting up directories for working files: binaries, templates, and so on.
+*   Creating a corresponding ``tt.yaml`` :ref:`configuration file <tt-config_file>`.
+
+Details
+-------
+
+``tt init`` checks the existence of configuration files for Cartridge (``cartridge.yml``)
+or the ``tarantoolctl`` utility (``.tarantoolctl``) in the current directory.
+If such files are found, ``tt`` generates an environment that uses the same
+directories:
+
+*   ``cartridge.yml`` -- the directories specified in the file.
+*   ``.tarantoolctl`` -- the directories specified in the ``default_cfg`` table.
+
+    .. note::
+
+        ``init`` is the only ``tt`` command that invokes ``.tarantoolctl`` files.
+        Thus, variables defined in this script will not be available in
+        applications launched by a ``tt start`` call.
+
+If there is no ``cartridge.yml`` or ``.tarantoolctl`` files in the current directory,
+``tt init`` creates a default environment in it. This includes creating the
+following directories and files:
+
+*   ``bin`` -- the directory for storing binary files.
+*   ``include`` -- the directory for storing  header files.
+*   ``distfiles`` -- the directory for storing installation files.
+*   ``instances.enabled`` -- the directory for storing running applications or symlinks.
+*   ``modules`` -- the directory for storing external modules.
+*   ``tt.yaml`` -- the configuration file.
+*   ``templates`` -- the directory for storing application templates.
+
+
+Example
+--------
+
+Create a ``tt`` environment in the current directory:
+
+..  code-block:: bash
+
+    tt init