Update Makefile and manual page

Signed-off-by: Shin'ya Minazuki <shinyoukai@laidback.moe>

Makefile

@@ -8,3 +8,10 @@ build:
 	@${GO} build ${GOFLAGS}
 clean:
 	@rm -f mikuru
+install:
+	install -d ${DESTDIR}${PREFIX}/bin
+	install -d ${DESTDIR}${PREFIX}/man/man1
+	install -m0755 mikuru ${DESTDIR}${PREFIX}/bin
+	install -m0660 mikuru.1 ${DESTDIR}${PREFIX}/man/man1
+tidy:
+	@${GO} mod tidy

mikuru.1

@@ -1,4 +1,4 @@
-.Dd December 30, 2025
+.Dd January 21, 2026
 .Dt MIKURU 1
 .Os
 .Sh NAME
@@ -26,5 +26,7 @@ and will fail if the variable is unset.
 .El
 .Sh FILES
 .Pa ~/.config/mikuru.ini
+.Sh LICENSE
+This work is licensed under the terms of the Internet Systems Consortium License
 .Sh AUTHORS
 .An Shin'ya Minazuki Aq Mt shinyoukai@laidback.moe