'make clean' should only remove the generated html files, index.html is not

one of them!

docs/Makefile.am

@@ -8,10 +8,11 @@ man_MANS = \
 	curl.1 \
 	curl-config.1
 
-HTMLPAGES = \
+GENHTMLPAGES = \
 	curl.html \
-	curl-config.html \
-	index.html
+	curl-config.html
+
+HTMLPAGES = $(GENHTMLPAGES) index.html
 
 PDFPAGES = \
 	curl.pdf \
@@ -19,7 +20,7 @@ PDFPAGES = \
 
 SUBDIRS = examples libcurl
 
-CLEANFILES = $(HTMLPAGES) $(PDFPAGES)
+CLEANFILES = $(GENHTMLPAGES) $(PDFPAGES)
 
 EXTRA_DIST = MANUAL BUGS CONTRIBUTE FAQ FEATURES INTERNALS SSLCERTS	\
 	     README.win32 RESOURCES TODO TheArtOfHttpScripting THANKS	\