build: Add INSTALL.md and update "make help"

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

INSTALL.md

+## Installing CRIU from source code
+
+Once CRIU is built one can easily setup the complete CRIU package
+(which includes executable itself, CRIT tool, libraries, manual
+and etc) simply typing
+
+    make install
+
+this command accepts the following variables:
+
+ * **DESTDIR**, to specify global root where all components will be placed under (`/` by default);
+ * **PREFIX**, to specify additional prefix for path of every component installed (`/usr/local` by default);
+ * **BINDIR**, to specify where to put CRIT tool (`$(PREFIX)/bin` by default);
+ * **SBINDIR**, to specify where to put CRIU executable (`$(PREFIX)/sbin` by default);
+ * **MANDIR**, to specify directory for manual pages (`$(PREFIX)/share/man` by default);
+ * **SYSTEMDUNITDIR**, to specify place where systemd units are living (`$(PREFIX)/lib/systemd/system` by default);
+ * **LIBDIR**, to specify directory where to put libraries (`$(PREFIX)/lib` by default).
+
+Thus one can type
+
+    make DESTDIR=/some/new/place install
+
+and get everything installed under `/some/new/place`.
+
+## Uninstalling CRIU
+
+To clean up previously installed CRIU instance one can type
+
+    make uninstall
+
+and everything should be removed. Note though that if some variable (**DESTDIR**, **BINDIR**
+and such) has been used during installation procedure, the same *must* be passed with
+uninstall action.

Makefile

@@ -228,7 +228,8 @@ help:
 	@echo '    * criu            - Build criu'
 	@echo '      zdtm            - Build zdtm test-suite'
 	@echo '      docs            - Build documentation'
-	@echo '      install         - Install binary and man page'
+	@echo '      install         - Install CRIU (see INSTALL.md)'
+	@echo '      uninstall       - Uninstall CRIU'
 	@echo '      dist            - Create a source tarball'
 	@echo '      clean           - Clean most, but leave enough to navigate'
 	@echo '      mrproper        - Delete all compiled/generated files'