add apk-cache(8)

doc/Makefile

@@ -6,6 +6,7 @@ $(obj)/%.8: $(src)/%.8.scd
 
 docs: $(obj)/apk.8 \
 	$(obj)/apk-add.8 \
+	$(obj)/apk-cache.8 \
 	$(obj)/apk-del.8 \
 	$(obj)/apk-fix.8 \
 	$(obj)/apk-update.8 \

doc/apk-cache.8.scd

@@ -0,0 +1,41 @@
+apk-cache(8)
+
+# NAME
+
+apk cache - manage a local cache of package files
+
+# SYNOPSIS
+
+*apk cache* [<_options_>...] clean
+
+*apk cache* [<_options_>...] download
+
+*apk cache* [<_options_>...] sync
+
+# DESCRIPTION
+
+*apk cache download* will fetch package files from the repositories and store
+them in the cache, which must be enabled upfront (see *apk-cache*(5)).
+
+*apk cache clean* will remove package files which are no longer necessary,
+having been made obsolete by new versions or no longer being transitively
+depended on by packages in _world_.
+
+*apk cache sync* performs both operations.
+
+# OPTIONS
+
+*-l, --latest*
+	Disables normal heuristics for choosing which repository to install a
+	package from, preferring only repositories from which the latest
+	version is available. This has no effect on pinned packages.
+
+*-u, --upgrade*
+	When caching packages which are already installed, prefer their upgrades
+	rather than considering the requirement fulfilled by the current
+	installation.
+
+# AUTHORS
+
+Natanael Copa <ncopa@alpinelinux.org>++
+Timo Teräs <_timo.teras@iki.fi_>