Updating for Hugo 15 patch

Signed-off-by: Mary Anthony <mary@docker.com>

docs/Dockerfile

@@ -1,4 +1,4 @@
-FROM docs/base:latest
+FROM docs/base:hugo-github-linking
 MAINTAINER Mary Anthony <mary@docker.com> (@moxiegirl)
 
 ENV PROJECT=registry
@@ -7,17 +7,3 @@ ENV PROJECT=registry
 COPY . /src
 
 COPY . /docs/content/$PROJECT/
-
-# Processing GitHub Markdown
-# 1 Remove <!--[metadata]> and <![end-metadata]-->
-# 2 Remove any leading combination of dots and slashes (./, ../, ../../, etc)
-# 3 Prepend /$PROJECT to all links, remove any trailing .md, only for non http:// links and non internal anchors
-
-RUN find /docs/content/$PROJECT -type f -name "*.md" -not -name "*.compare.md" -exec sed -i.old \
-    -e '/^<!\(--\)\{0,1\}\[\(end-\)\{0,1\}metadata\]\(--\)\{0,1\}>/g' \
-    -e 's/\(\][(]\)\(\.*\/\)*/\1/g' \
-    -e 's/\(\][(]\)\([A-Za-z0-9_/-]\{1,\}\)\(\.md\)\{0,1\}\(#\{0,1\}\(#[A-Za-z0-9_-]*\)\{0,1\}\)[)]/\1\/'$PROJECT'\/\2\4)/g' \
-        {} \;
-
-# Prepare the compare file and expect an empty diff against test.md
-RUN sed -i.old -e 's/\/placeholder\//\/'$PROJECT'\//g' /docs/content/$PROJECT/test.compare.md && diff -u /docs/content/$PROJECT/test.md /docs/content/$PROJECT/test.compare.md