remove requirements.txt and update readme.md

Author: satoshi03

MANIFEST.ini

@@ -1,3 +1,2 @@
 include info.py
 include version.py
-include requirements.txt

README.md

@@ -34,7 +34,7 @@ In case that you want to send a custom message:
 > slackbot.notify(text="Tako is a sushi", channel="#sushi", username="sushi-bot", icon_emoji=":sushi:")
 </pre>
 
-If you want to use richly-formatted massages.
+If you want to use richly-formatted massages:
 
 <pre>
 > attachments = []
@@ -43,3 +43,8 @@ If you want to use richly-formatted massages.
 > slackbot.notify(attachments=attachments)
 </pre>
 
+More detail description of message formatting, refer according pages:
+
+- [Message Formatting](https://api.slack.com/docs/formatting)
+- [Attachments](https://api.slack.com/docs/attachments)
+

requirements.txt

@@ -15,7 +15,6 @@
 setup_options = info.INFO
 setup_options["version"] = version.VERSION
 setup_options.update(dict(
-  install_requires = open('requirements.txt').read().splitlines(),
   packages         = ['slackbot'],
 ))