added README.md

README.md

@@ -1,2 +1,23 @@
 # pom
 Phases Of Moon - calculate when the next Full Moon will be
+
+I have been using https://metacpan.org/pod/Astro::MoonPhase
+since 2007 in a small perl wrapper called pom.
+
+I thought that I should port it to Rust and this is my
+first attempt. It was surprisingly easy. I expect that it
+might be possible to automate porting many perl modules
+to Rust.
+
+# performance
+```txt
+perl> time pom # ver. 0.2
+real    0m0.022s
+user    0m0.022s
+sys     0m0.000s
+
+rust> time pom # ver. 0.3
+real    0m0.002s
+user    0m0.002s
+sys     0m0.001s
+```