Readme instructions do not produce correct Signature Hash

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### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [ x ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

### Minimal steps to reproduce
> Our customers follow the directions in readme file to connect to their own tenant
-clone the repository
-build in Android studio
-create App Registration in Azure Portal
-create redirect Uri using the package name and Hash generated from the Azure Portal instructions
-create json config file and intent-filter based on the information generated in the Azure Portal

### Any log messages given by the failure
> This produces an Msal exception:
com.microsoft.identity.client.exception.MsalClientException: The redirect URI in the configuration file doesn't match with the one generated with package name and signature hash. Please verify the uri in the config file and your app registration in Azure portal.

### Expected/desired behavior
> Our customers should be able to get our fundamental sample working with their own tenant by following the directions in the readme and official documentation

### OS and Version?
> Any recent version of Android

### Versions
> 2.21

### Mention any other details that might be useful

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Hi Team!

I am a Microsoft Support Engineer who supports Msal. Our customers are frustrated with this sample because it cannot successfully build the PublicClientApplication when the customers follow our readme and official documentation to use it with their own tenant.

The reason for this is that the sample contains its own keystore and points to this keystore in the build files. The official guidance on getting a debug Signature Hash will produce the default debug Hash for the customer's instance of Android Studio; however, this sample builds with its own Signature Hash. So by following our guidance, the customer is actually using the incorrect Signature Hash to generate a redirect Uri and intent filter.

This can be resolved by explicitly explaining how our customers can customize their keytool command specifically for this sample. (Basically the customer needs to change the path to point to the project's keystore).
Even just pointing out the fact that the sample uses its own keystore and the customer will need to adjust the keytool command will be a great improvement.

Step 5 in the portion in the readme about using your own App Registration might be a good place for this:

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