Remove Sourcetree recommandation

Author: ilg-ul

README-DEVELOP.md

@@ -143,9 +143,9 @@ it to your favourite tools.
 ### Git client
 
 For macOS and Windows, the recommended Git client is
-[Sourcetree](https://www.sourcetreeapp.com/).
+[Fork](https://fork.dev).
 
-Since Sourcetree is not available for GNU/Linux, another choice is
+Since Fork is not available for GNU/Linux, another choice is
 Git Kraken, which can be downloaded for free from
 [gitkraken.com](https://www.gitkraken.com/download).
 

README-RELEASE.md

@@ -78,7 +78,7 @@ In the qemu.git fork:
 
 ### Update helper
 
-With Sourcetree, go to the helper repo and update to the latest master commit.
+With a git client, go to the helper repo and update to the latest master commit.
 
 ## Build