fix: use relative urls when github publish enabled

docs: add doc about enabling relative urls when github

docs/settings.rst

@@ -445,6 +445,7 @@ This would save your articles into something like
    Defines whether Pelican should use document-relative URLs or not. Only set
    this to ``True`` when developing/testing and only if you fully understand
    the effect it can have on links/feeds.
+   This option is enabled by default if you use github pages.
 
 .. data:: ARTICLE_URL = '{slug}.html'
 

pelican/tools/templates/Makefile.jinja2

@@ -45,7 +45,12 @@ ifeq ($(DEBUG), 1)
 	PELICANOPTS += -D
 endif
 
+{% if github %}
+RELATIVE ?= 1
+{% else %}
 RELATIVE ?= 0
+{% endif %}
+
 ifeq ($(RELATIVE), 1)
 	PELICANOPTS += --relative-urls
 endif

pelican/tools/templates/publishconf.py.jinja2

@@ -9,7 +9,12 @@ from pelicanconf import *
 
 # If your site is available via HTTPS, make sure SITEURL begins with https://
 SITEURL = "{{siteurl}}"
+
+{{ if github }}
 RELATIVE_URLS = False
+{{ else }}
+RELATIVE_URLS = True
+{{ endif }}
 
 FEED_ALL_ATOM = "feeds/all.atom.xml"
 CATEGORY_FEED_ATOM = "feeds/{slug}.atom.xml"