[FIX] README template section levels

The README generation could return an error like this:

  docutils.utils.SystemMessage: account_avatax/README.rst:349: (SEVERE/4)
  Title level inconsistent:

  Authors
  ~~~~~~~

In fact the Authors section is inside a Credits first level title, ``====``,
and should be a second level title, ``----``,
instead of a third level, ``~~~``.

Author: dreispt

tests/data/readme_tests/addon1/README.expected-acme

@@ -86,23 +86,23 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Contributors
-~~~~~~~~~~~~
+------------
 
 * contributor1
 * contributor2
 
 Other credits
-~~~~~~~~~~~~~
+-------------
 
 This module has been funded by Acme Corp.
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 This module is part of the `acme/server-tools <https://github.com/acme/server-tools/tree/12.0/addon1>`_ project on GitHub.
 

tests/data/readme_tests/addon1/README.expected-oca

@@ -92,23 +92,23 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Contributors
-~~~~~~~~~~~~
+------------
 
 * contributor1
 * contributor2
 
 Other credits
-~~~~~~~~~~~~~
+-------------
 
 This module has been funded by Acme Corp.
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 This module is maintained by the OCA.
 

tests/data/readme_tests/addon_one_maintainer/README.expected-acme

@@ -47,12 +47,12 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 .. |maintainer-toto| image:: https://github.com/toto.png?size=40px
     :target: https://github.com/toto

tests/data/readme_tests/addon_one_maintainer/README.expected-oca

@@ -53,12 +53,12 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 This module is maintained by the OCA.
 

tests/data/readme_tests/addon_two_maintainers/README.expected-acme

@@ -40,12 +40,12 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 .. |maintainer-toto| image:: https://github.com/toto.png?size=40px
     :target: https://github.com/toto

tests/data/readme_tests/addon_two_maintainers/README.expected-oca

@@ -46,12 +46,12 @@ Credits
 =======
 
 Authors
-~~~~~~~
+-------
 
 * Acme Inc
 
 Maintainers
-~~~~~~~~~~~
+-----------
 
 This module is maintained by the OCA.
 

tools/gen_addon_readme.template

@@ -61,17 +61,17 @@ Credits
 
 {% if authors -%}
 Authors
-~~~~~~~
+-------
 
 {% for author in authors -%}
 * {{ author }}
 {% endfor %}
 {% endif -%}
 
-{{ fragment('CONTRIBUTORS', 'Contributors', sub='~') }}
-{{- fragment('CREDITS', 'Other credits', sub='~') -}}
+{{ fragment('CONTRIBUTORS', 'Contributors', sub='-') }}
+{{- fragment('CREDITS', 'Other credits', sub='-') -}}
 Maintainers
-~~~~~~~~~~~
+-----------
 {%- if org_name == 'OCA' %}
 
 This module is maintained by the OCA.