docs: fixed link, added readme (#21953)

* docs: fixed links

* docs: added Readme to test locally

README.md

@@ -0,0 +1,7 @@
+# Documentation of the go-ethereum website
+
+To start a jekyll server run:
+```shell
+docker-compose up
+```
+Now you can visit `localhost:4000` to look at the site.

docs/_getting-started/private-net.md

@@ -9,7 +9,7 @@ controlled ethereum network is useful as a backend for network integration testi
 developers working on issues related to networking/blockchain synching/message
 propagation, etc or DAPP developers testing multi-block and multi-user scenarios).
 
-We assume you are able to build `geth` following the [build instructions](../install-and-build/installing-geth)
+We assume you are able to build `geth` following the [build instructions](../docs/install-and-build/installing-geth)
 
 ## Setting up multiple nodes