Add installation steps of heroku on windows. (#481)

For windows, on git bash, heroku login don't work, hence use winpty heroku login. Refer heroku/cli#84. Similar PR raised in badgeyay fossasia/badgeyay#531 .

docs/installation/heroku.md

@@ -8,9 +8,9 @@ One-click Heroku deployment is available:
 
 * We need to install heroku on our machine. Type the following in your linux terminal:
 	* ```wget -O- https://toolbelt.heroku.com/install-ubuntu.sh | sh```
-  This installs the Heroku Toolbelt on your machine to access heroku from the command line.
+  This installs the Heroku Toolbelt on your machine to access heroku from the command line. For windows user, install from [here](https://devcenter.heroku.com/articles/heroku-cli#windows)
 * Next we need to login to our heroku server (assuming that you have already created an account). Type the following in the terminal:
-	* ```heroku login```
+	* ```heroku login```(for windows user on cygwin or git bash: ```winpty heroku login```)
     * Enter your credentials and login.
 * Once logged in we need to create a space on the heroku server for our application. This is done with the following command
 	* ```heroku create```
@@ -27,4 +27,4 @@ One-click Heroku deployment is available:
 
 * Then we deploy the code to heroku.
 	* ```git push heroku master``` or
-    * ```git push heroku yourbranch:master``` if you are in a different branch than master
+    * ```git push heroku yourbranch:master``` if you are in a different branch than master