Changed http:// to https:// on readthedocs links in README.md (ethere…

…um#2313)

Changed http:// to https:// on readthedocs links in README.md

README.md

@@ -2,7 +2,7 @@
 [![Join the chat at https://gitter.im/ethereum/solidity](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/ethereum/solidity?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 ## Useful links
-To get started you can find an introduction to the language in the [Solidity documentation](https://solidity.readthedocs.org). In the documentation, you can find [code examples](http://solidity.readthedocs.io/en/latest/solidity-by-example.html) as well as [a reference](http://solidity.readthedocs.io/en/latest/solidity-in-depth.html) of the syntax and details on how to write smart contracts.
+To get started you can find an introduction to the language in the [Solidity documentation](https://solidity.readthedocs.org). In the documentation, you can find [code examples](https://solidity.readthedocs.io/en/latest/solidity-by-example.html) as well as [a reference](https://solidity.readthedocs.io/en/latest/solidity-in-depth.html) of the syntax and details on how to write smart contracts.
 
 You can start using [Solidity in your browser](https://ethereum.github.io/browser-solidity/) with no need to download or compile anything.
 
@@ -11,9 +11,9 @@ The changelog for this project can be found [here](https://github.com/ethereum/s
 Solidity is still under development. So please do not hesitate and open an [issue in GitHub](https://github.com/ethereum/solidity/issues) if you encounter anything strange.
 
 ## Building
-See the [Solidity documentation](http://solidity.readthedocs.io/en/latest/installing-solidity.html#building-from-source) for build instructions.
+See the [Solidity documentation](https://solidity.readthedocs.io/en/latest/installing-solidity.html#building-from-source) for build instructions.
 
 ## How to Contribute
-Please see our contribution guidelines in [the Solidity documentation](http://solidity.readthedocs.io/en/latest/contributing.html).
+Please see our contribution guidelines in [the Solidity documentation](https://solidity.readthedocs.io/en/latest/contributing.html).
 
 Any contributions are welcome!