Fix wrong flag for Pypi nightly repository

We should use `--extra-index-url` to specify extra index for Python packages, instead of `-i`.

PiperOrigin-RevId: 448149226

Author: tfx-copybara

README.md

@@ -45,7 +45,7 @@ Google Cloud. To install the latest nightly package, please use the following
 command:
 
 ```bash
-pip install -i https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
+pip install --extra-index-url https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
 ```
 
 This will install the nightly packages for the major dependencies of TFDV such

RELEASE.md

@@ -542,7 +542,7 @@
     following command:
 
     ```
-    pip install -i https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
+    pip install --extra-index-url https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
     ```
 
     Note: These nightly packages are unstable and breakages are likely to

g3doc/install.md

@@ -47,7 +47,7 @@ Google Cloud. To install the latest nightly package, please use the following
 command:
 
 ```bash
-pip install -i https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
+pip install --extra-index-url https://pypi-nightly.tensorflow.org/simple tensorflow-data-validation
 ```
 
 This will install the nightly packages for the major dependencies of TFDV such