build: Add DISABLE_DOCS to skip man pages

When bootc is built from source and its `make install` tree is copied
into a minimized image, the man pages end up in an image that excludes
documentation everywhere else: Fedora container images set
`tsflags=nodocs` for dnf, Ubuntu minimized images exclude
/usr/share/man for dpkg. A distro package goes through that filter, a
source build doesn't, so the Makefile is where that choice has to be
made.

Setting DISABLE_DOCS=1 skips generating and installing the man pages.
This also skips the extra docgen-featured build of bootc, and the
dependency on go-md2man. The name and check follow skopeo's Makefile,
which has the same switch. The default is unchanged, so packaging
isn't affected. Files under /usr/share/doc/bootc are still installed:
they're base image configuration, not documentation.

While there, add the missing section 7 to the man page directories
listed in the packaging docs.

Moving the man pages to a separate install target was considered and
discarded: the man pages have to be built before the binary, so that
the production build overwrites the docgen one in target/release (see
e747216, "cli: Fix rhsm feature propagation and manpage build order").

Assisted-by: AI
Signed-off-by: Franck Cuny <franck@fcuny.net>

Author: fcuny

Makefile

@@ -49,10 +49,21 @@ CARGO_FEATURES ?= $(CARGO_FEATURES_DEFAULT)
 # again. The unit test targets (install-unit-tests) don't use this and always
 # build with the default features.
 CARGO_OPTIONS ?= --features "$(CARGO_FEATURES)"
+# Set to 1 to skip generating and installing man pages, e.g. for source
+# builds into images that exclude documentation:
+#   make install DISABLE_DOCS=1
+# This doesn't affect $(prefix)/share/doc/bootc/baseimage, which holds base
+# image configuration rather than documentation.
+DISABLE_DOCS ?=
 
 # Build all binaries
 .PHONY: bin
+# The man pages are built first so that the production binary below
+# overwrites the docgen-featured one in target/release.
+ifneq ($(DISABLE_DOCS),1)
 bin: manpages
+endif
+bin:
 	cargo build --release $(CARGO_OPTIONS) --bins
 
 # The docgen feature this adds implies install-to-disk, so the man pages
@@ -77,9 +88,11 @@ install: completion
 	ln -s "$(STORAGE_RELATIVE_PATH)" "$(DESTDIR)$(prefix)/lib/bootc/storage"
 	install -D -m 0755 crates/cli/bootc-generator-stub $(DESTDIR)$(prefix)/lib/systemd/system-generators/bootc-systemd-generator 
 	install -d $(DESTDIR)$(prefix)/lib/bootc/install
+ifneq ($(DISABLE_DOCS),1)
 	install -D -m 0644 -t $(DESTDIR)$(prefix)/share/man/man5 target/man/*.5
 	install -D -m 0644 -t $(DESTDIR)$(prefix)/share/man/man7 target/man/*.7
 	install -D -m 0644 -t $(DESTDIR)$(prefix)/share/man/man8 target/man/*.8
+endif
 	install -D -m 0644 target/completion/bootc.bash $(DESTDIR)$(prefix)/share/bash-completion/completions/bootc
 	install -D -m 0644 target/completion/bootc.elvish $(DESTDIR)$(prefix)/share/elvish/lib/bootc.elv
 	install -D -m 0644 target/completion/bootc.fish $(DESTDIR)$(prefix)/share/fish/vendor_completions.d/bootc.fish

docs/src/bootc-packaging-and-integration.7.md

@@ -35,12 +35,23 @@ make install DESTDIR=/path/to/staging/root
 
 The install target handles:
 - Binary installation to `$(prefix)/bin`
-- Man pages to `$(prefix)/share/man/man{5,8}`
+- Man pages to `$(prefix)/share/man/man{5,7,8}`
 - systemd units to `$(prefix)/lib/systemd/system`
 - Documentation and examples to `$(prefix)/share/doc/bootc`
 - Dracut module to `/usr/lib/dracut/modules.d/51bootc`
 - Base image configuration files
 
+To skip building and installing the man pages, for example when building
+from source into a container image that excludes documentation, set
+`DISABLE_DOCS=1`:
+
+```bash
+make install DISABLE_DOCS=1 DESTDIR=/path/to/staging/root
+```
+
+This also drops the build-time dependency on `go-md2man`. The base image
+files under `$(prefix)/share/doc/bootc` are still installed.
+
 ### Optional Installation Targets
 
 #### install-ostree-hooks