userguide/Makefile: don't add "install" to EXTRA_DIST

Adding the directory "install" to EXTRA_DIST, actually triggers make
to run "make install", which is not what we want. Instead, avoid this
magic keyword and list the files in the install directory
individually.

If the user doesn't have permission to install files to the prefix,
like "/usr", then "make dist" can fail. Worse, even they do have
permission to write into the prefix, a "make dist" will install files
there when it shouldn't.

Ticket: #8279

doc/userguide/Makefile.am

@@ -1,3 +1,7 @@
+# Don't simply use the directory "install" to include the files in
+# install/. That name in EXTRA_DIST triggers "make dist" to run "make
+# install". Which can lead to a permission denied error, or worse,
+# files actually installed when they shouldn't be.
 EXTRA_DIST = \
 	_generated \
 	_static \
@@ -17,7 +21,11 @@ EXTRA_DIST = \
 	upgrade.rst \
 	initscripts.rst \
 	install.rst \
-	install \
+	install/debian.rst \
+	install/other.rst \
+	install/rpm.rst \
+	install/ubuntu.rst \
+	install/windows.rst \
 	ips \
 	licenses \
 	lua \