Makefile: make help: remove <package>- help, add link to online manual

We only documented a few of the <package>- targets and it's hard to
decide which ones are relevant for make help. Since the help is already
way too long, it's better to remove these advanced targets.

Instead, let's refer to the online manual.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -847,9 +847,6 @@ help:
 	@echo 'Build:'
 	@echo '  all                    - make world'
 	@echo '  toolchain              - build toolchain'
-	@echo '  <package>-rebuild      - force recompile <package>'
-	@echo '  <package>-reconfigure  - force reconfigure <package>'
-	@echo '  <package>-graph-depends    - generate graph of the dependency tree for package'
 	@echo
 	@echo 'Configuration:'
 	@echo '  menuconfig             - interactive curses-based configurator'
@@ -912,7 +909,8 @@ ifneq ($(wildcard $(BR2_EXTERNAL)/configs/*_defconfig),)
 	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
 endif
 	@echo
-	@echo 'See docs/README, or generate the Buildroot manual for further details'
+	@echo 'For further details, see README, generate the Buildroot manual, or consult'
+	@echo 'it on-line at http://buildroot.org/docs.html'
 	@echo
 
 release: OUT = buildroot-$(BR2_VERSION)