Remove git clone and directory summary (MystenLabs#1375)

* Remove git clone and directory summary

Move git clone and directory summary from Contribute to Sui to Install Sui

* Update index.md

Add #source-code named anchor to link for easy reference

doc/src/contribute/index.md

@@ -29,22 +29,10 @@ You may also suggest changes to the docs directly in GitHub right here using the
 
 Simply edit the file in question and generate a pull request. We will get back to you shortly.
 
-## Download and learn Sui
+## Download Sui
 
-In order to obtain the Sui source code, clone the Sui repository:
-
-```shell
-git clone https://github.com/MystenLabs/sui.git
-```
-
-You can start exploring Sui's source code by looking into the following primary directories:
-
-* [sui](https://github.com/MystenLabs/sui/tree/main/sui) - the Sui binaries (`wallet`, `sui-move`, and more)
-* [sui_programmability](https://github.com/MystenLabs/sui/tree/main/sui_programmability) - Sui's Move language integration also including games and other Move code examples for testing and reuse
-* [sui_core](https://github.com/MystenLabs/sui/tree/main/sui_core) - authority server and Sui Gateway
-* [sui_types](https://github.com/MystenLabs/sui/tree/main/sui_types) - coins, gas, and other object types
-* [explorer](https://github.com/MystenLabs/sui/tree/main/explorer) - object explorer for the Sui network
-* [network_utils](https://github.com/MystenLabs/sui/tree/main/network_utils) - networking utilities and related unit tests
+In order to obtain the Sui source code, follow the steps to download (`git clone`) the `sui` repository
+at [Install Sui](../build/install.md#source-code).
 
 ## Send pull requests