add Makefile with tests and helpers, update/simplify #Contributing

 * make noexternallink: chekc for Lines with no source/demo/other link
 * make missinglicenselanguage: check Lines with only 1 or no language/license entry
 * make contrib: print list of contributors
 * make add: helper to add a new software entry
 * add TODOs
 * remove link to form since it is unmaintained and outputs wrongly formatted entries https://github.com/Kickball/awesome-selfhosted/issues/282#issuecomment-185423033
 * add BEGIN/END SOFTWARE LIST markers to restrict processing to software list only (HTML comments, not rendered to markdown)
 * link to README.md editor, issues, pull requests
 * Requirements for Makefile: make, bash. Available in Linux distribution repositories, in XCode on Mac, in GOW on Windows.
 * Fixes #461

Makefile

@@ -0,0 +1,45 @@
+#!/usr/bin/make -f
+SHELL = /bin/bash
+all: checks
+
+checks: missinglicenselanguage
+
+noexternallink:
+	@echo "Lines with no source/demo/other link:"
+	@sed -n -e '/BEGIN SOFTWARE LIST/,/END SOFTWARE LIST/ p' README.md | egrep '^ *\* ' | egrep --color=always '[a-z\.] `'
+
+missinglicenselanguage:
+	@echo "Lines with only 1 or no language/license entry:"
+	@sed -n -e '/BEGIN SOFTWARE LIST/,/END SOFTWARE LIST/ p' README.md | egrep '^ *\* ' | egrep -v '` `'
+
+contrib:
+	@git shortlog -sne
+
+add:
+	@#add a new entry
+	@printf 'Software name: ' ;\
+	read Name; if [ -z "$$Name" ]; then printf 'Missing software name!\n'; exit 1 ; fi ;\
+	printf 'Homepage URL: ' ;\
+	read Url; if [ -z "$$Url" ]; then printf 'Missing main project URL!\n'; exit 1 ; fi ;\
+	printf 'Description (max 250 char): ' ;\
+	read Description; if [ -z "$$Description" ]; then printf 'Missing description!\n'; exit 1 ; fi ;\
+	printf 'License: ' ;\
+	read License; if [ -z "$$License" ]; then printf 'Missing license!\n'; exit 1 ; fi ;\
+	printf 'Main server-side language/platform/requirement: ' ;\
+	read Language; if [ -z "$$Language" ]; then printf 'Missing language!\n'; exit 1 ; fi ;\
+	printf 'Demo URL (if any): ' ;\
+	read Demo; if [ -z "$$Demo" ]; then CDemo="" ; else CDemo="[Demo]($$Demo)" ; fi ;\
+	printf 'Source code URL (if different from Homepage): ' ;\
+	read Source; if [ -z "$$Source" ]; then CSource="" ; else CSource="[Source Code]($$Source)" ; fi ;\
+	if [[ "$$CSource" == "" && "$$Demo" == "" ]]; \
+	then Moreinfo="";\ printf "debug" ;\
+	else Moreinfo=$$(echo "($$CSource$$CDemo)" | sed 's|)\[|\], [|g') ;\
+	fi ;\
+	echo -e "Copy this entry to your clipboard, paste it in the appropriate category:\n\n" ;\
+	echo " * [$$Name]($$Url) - $${Description}. $$Moreinfo \`$$License\` \`$$Language\`"
+
+
+#TODO ask for category and insert item accordingly
+#TODO check for unsorted entries
+#TODO automatically sort entries/sections
+#TODO autoupdate contributors list