Allow wrapping for ARM table content

RTD style default never wraps <th> and <td> elements and that just does
not work for real sentences or any other long lines.

We can reconsider styling some tables separately, but at the moment we
do not have use for tables with long but unwrappable lines so it's
easier to allow wrapping globally.

doc/arm/conf.py

@@ -154,6 +154,10 @@ master_doc = 'index'
 # a list of builtin themes.
 #
 html_theme = 'sphinx_rtd_theme'
+html_static_path = ['_static']
+html_css_files = [
+    'custom.css'
+]
 
 # -- Options for EPUB output -------------------------------------------------