Update release version in quickstart.md (#303)

#### Motivation

Missed to update on doc in previous round.

#### Modifications

Edit the `docs/quickstart.md` file, updating the `RELEASE` variable in the "Get the latest release" section to the new release branch name.

#### Result

Correct version of release branch in Quickstart guide

/cc @njhill 
/assign @njhill 


Signed-off-by: Christian Kadner <ckadner@us.ibm.com>

docs/quickstart.md

@@ -13,7 +13,7 @@ To quickly get started using ModelMesh Serving, here is a brief guide.
 ### Get the latest release
 
 ```shell
-RELEASE=release-0.9
+RELEASE=release-0.10
 git clone -b $RELEASE --depth 1 --single-branch https://github.com/kserve/modelmesh-serving.git
 cd modelmesh-serving
 ```