docs: fix all internal cross-references after restructure

scripts/server-install.sh

@@ -25,6 +25,7 @@ cd "$WEBROOT"
 wget --no-verbose "https://getgrav.org/download/core/grav-admin/${GRAV_VERSION}${GRAV_CHANNEL_SUFFIX:-}" -O grav-admin.zip
 unzip -oq grav-admin.zip
 cp -rf grav-admin/. .
+cp -rf grav-admin/user/plugins/admin2 /tmp/admin2-plugin
 rm -rf grav-admin grav-admin.zip
 
 echo "==> Cloning user repo"
@@ -41,6 +42,8 @@ fi
 
 echo "==> Creating required directories"
 mkdir -p user/plugins user/accounts user/data
+cp -rf /tmp/admin2-plugin user/plugins/admin2
+rm -rf /tmp/admin2-plugin
 
 echo "==> Installing plugins"
 php bin/gpm install $PLUGINS -y