Link fix on Who are using unitsnet tab. (angularsen#1605)

On Readme.md, there was a misleading inner link on "Who are using
UnitsNet" tab.
I simply fixed that inner link.

Author: meokullu

README.md

@@ -31,7 +31,7 @@ New units will be backported to  `maintenance/v5` until v6 becomes stable.
 * [Serialize to JSON, XML and more](#serialize-to-json-xml-and-more)
 * [Want To Contribute?](#want-to-contribute)
 * [Continuous Integration](#continuous-integration)
-* [Who are Using This?](#who-are-using-this)
+* [Who are Using This?](#who-are-using-unitsnet)
 * [Top Usages by GitHub Repos](#top-usages-by-gitHub-repos)
 * [Units.NET on other platforms](#unitsnet-on-other-platforms)