Improve documentation

README.md

@@ -14,6 +14,32 @@ bidified_html = Bidify.bidify(html_input)
 # bidified_html: '<p dir="auto">some content even in nested format</p>' 
 ```
 
+# Rules
+
+The `dir="auto"` attribute should be applied on "bidifiable" tags as per the following rules:
+
+- Only apply on "bidifiable" tags.
+- All top-level elements
+- All child elements except the first child
+
+Bidifiable elements can be defined as per the use case requirements (not yet implemented).
+The default bidifiable tags are: `div`, `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `p`, `ul`, `ol`, `blockquote`.
+
+Notice that `li` elements shouldn't get `dir=auto` otherwise, the list appearance gets damaged.
+
+As a complementary step, CSS styles should use [logical properties](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_logical_properties_and_values). Here are a few examples:
+
+```css
+/* Physical properties */
+text-align: left;
+padding-right: 10px;
+border-left: 1px;
+/* Logical properties */
+text-align: start;
+padding-inline-end: 10px;
+border-inline-start: 1px;
+```
+
 ## License
 
 This project is a Free/Libre and Open Source software released under LGPLv3 license.