Merge branch 'qgis_doc' into 'develop'

Simplify the QGIS documentation

Closes #1903

See merge request orfeotoolbox/otb!564

Documentation/Cookbook/rst/QGISInterface.rst

 QGIS interface
 ==============
 
-The QGIS-OTB plugin (requires QGIS > 3.0)
+The QGIS-OTB plugin (requires QGIS > 3.2)
 -----------------------------------------
 
-With QGIS 3.0.2 or later, you will need to manually install the plugin.
-Clone qgis-otb-plugin repository and set ``QGIS_PLUGINPATH``:
+With QGIS < 3.8 you will need to manually install the plugin.
+You can follow the instruction here: https://gitlab.orfeo-toolbox.org/orfeotoolbox/qgis-otb-plugin#otb-provider-for-qgis-processing
 
-For Linux/Unix/MacOSX
-^^^^^^^^^^^^^^^^^^^^^
 
-::
-
-    mkdir $HOME/projects; cd $HOME/projects
-    git clone https://gitlab.orfeo-toolbox.org/orfeotoolbox/qgis-otb-plugin
-    export QGIS_PLUGINPATH=$HOME/projects/qgis-otb-plugin
-
-For Windows
-^^^^^^^^^^^
-
-Clone qgis-otb-plugin repository to ``C:\qgis-plugins\qgis-otb-plugin``
-
-::
-
-    git clone https://gitlab.orfeo-toolbox.org/orfeotoolbox/qgis-otb-plugin
-
-Then set the ``QGIS_PLUGINPATH`` variable:
-
-* System properties (``Windows Key + R -> sysdm.cpl`` ) 
-* Select Advanced Tab -> Environment variables. 
-* Under "user variables for " 
-* Add or Edit variable ``QGIS_PLUGINPATH`` and set value to ``C:\qgis-plugins\qgis-otb-plugin``
+With QGIS > 3.8, the plugin is in the QGIS core. So you just need install OTB and set the plugin up.
 
 Download and Install OTB
 ^^^^^^^^^^^^^^^^^^^^^^^^
@@ -59,27 +37,6 @@ You can see OTB under "Providers":
 * Set OTB application folder. This is location of your OTB applications. ``<OTB_FOLDER>/lib/otb/applications``
 * Click "ok" to save settings and close dialog. If settings are correct, you will have OTB algorithms loaded  in Processing toolbox
 
-Using the processing toolbox (for QGIS < 3.0)
----------------------------------------------
-
-In older QGIS version (3.0 or before), OTB applications are available from QGIS.
-Use them from the processing toolbox, which is accessible under `Processing
--> ToolBox`. Switch to “advanced interface” in the bottom of the
-application widget and OTB applications will be there.
-
-.. figure:: Art/QtImages/qgis-otb.png
-
-Using a custom OTB
-^^^^^^^^^^^^^^^^^^
-
-If QGIS cannot find OTB, the “applications folder” and “binaries folder”
-can be set from the settings found under Processing :math:`\rightarrow`
-Settings :math:`\rightarrow` “service provider”.
-
-.. figure:: Art/QtImages/qgis-otb-settings.png
-
-On some versions of QGIS, if an existing OTB installation is found, the
-textfield settings will not be shown. To use a custom OTB instead of the
-existing one, you will need to replace the otbcli, otbgui and library
-files in QGIS installation directly.
-
+Troubleshoot
+------------
+As of QGIS 3.8 the otb plugin is in the core. It might get messy if you have a previously installed plugin. Try to remove the old plugin before launching QGIS.