add description for blogging platforms category

- https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2984

README.md

@@ -199,6 +199,8 @@ _Related: [Internet of Things (IoT)](#internet-of-things-iot)_
 
 **[`^        back to top        ^`](#)**
 
+A [blog](https://en.wikipedia.org/wiki/Blog) is a discussion or informational website consisting of discrete, diary-style text entries (posts).
+
 _Related: [Static Site Generators](#static-site-generators), [Content Management Systems (CMS)](#content-management-systems-cms)_
 
 _See also: [WeblogMatrix](https://www.weblogmatrix.org/)_