add rudimentary man page

This is needed for "git latexdiff --help" to work.

Fixes #6.

Makefile

@@ -1,4 +1,5 @@
 gitexecdir = ${shell git --exec-path}
+gitmanpath = ${shell git --man-path}
 
 -include ./config.mak
 
@@ -9,18 +10,33 @@ endif
 BASH_PATH_SQ = $(subst ','\'',$(BASH_PATH))
 GIT_LATEXDIFF_VERSION=${shell git describe --tags HEAD}
 gitexecdir_SQ = $(subst ','\'',$(gitexecdir))
+gitmanpath_SQ = $(subst ','\'',$(gitmanpath))
 
 SCRIPT=git-latexdiff
 
-.PHONY: install help
+.PHONY: help install-bin install-doc install
 help:
 	@echo 'This is the help target of the Makefile. Current configuration:'
 	@echo '  gitexecdir = $(gitexecdir_SQ)'
 	@echo '  BASH_PATH = $(BASH_PATH_SQ)'
 	@echo 'Run "$(MAKE) install" to install $(SCRIPT) in gitexecdir.'
 
-install:
+install: install-bin install-doc
+
+install-bin:
 	sed -e '1s|#!.*/bash|#!$(BASH_PATH_SQ)|' \
 	    -e 's|@GIT_LATEXDIFF_VERSION@|$(GIT_LATEXDIFF_VERSION)|' \
 	        $(SCRIPT) > '$(gitexecdir_SQ)/$(SCRIPT)'
 	chmod 755 '$(gitexecdir_SQ)/$(SCRIPT)'
+
+git-latexdiff.txt: git-latexdiff git-latexdiff.txt.header
+	( cat git-latexdiff.txt.header ; \
+	  printf '%s\n' ------------ ; \
+	  ./git-latexdiff --help ; \
+	  printf '%s\n' ------------ ) > $@
+
+git-latexdiff.1: git-latexdiff.txt
+	a2x --doctype manpage --format manpage $<
+
+install-doc: git-latexdiff.1
+	cp $< $(gitmanpath_SQ)

git-latexdiff.txt.header

@@ -0,0 +1,9 @@
+git-latexdiff(1)
+================
+
+NAME
+----
+git-latexdiff - Call latexdiff on two Git revisions of a file
+
+OPTIONS
+-------