Fix 4177 set default yaml linters (#4178)

* Fix 4177 set default yaml linters

* Fix 4177 set default yaml linters

doc/ale-yaml.txt

@@ -13,6 +13,14 @@ Installation
 
 See installation guide: https://github.com/rhysd/actionlint#quick-start
 
+This linter is disabled by default and must be enabled byt setting `g:ale_linters`.
+To enable it only for Github Action YAML files a configuration like this is
+better:
+
+>
+ au BufRead,BufNewFile */.github/*/*.y.?ml let b:ale_linters = {'yaml': ['actionlint']}
+<
+
 Options
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