docs(guidelines): fix broken links

As pointed out here:

#391 (comment)

Author: wincent

guidelines/README.md

@@ -2,7 +2,7 @@
 
 ![guidelines](https://github.com/liferay/liferay-frontend-projects/workflows/guidelines/badge.svg)
 
-This is a live (changing) repository containing [general](/general) and [Liferay DXP-specific](/dxp) guidelines for doing Frontend Development at Liferay Inc.
+This is a live (changing) repository containing [general](general) and [Liferay DXP-specific](dxp) guidelines for doing Frontend Development at Liferay Inc.
 
 ## Guideline development