Add un-/install statement to `v3` to `v4` migration guide

[bennettdams]

This adds a statement to uninstall react-query and install @tanstack/react-query to the v3 to v4 migration guide.

[codesandbox-ci[bot]]

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Latest deployment of this branch, based on commit eb22d9e6183c0f85f0e82718eb7998408371fb38:

Sandbox	Source
@tanstack/query-example-react-basic	Configuration
@tanstack/query-example-react-basic-typescript	Configuration

[codecov-commenter]

Codecov Report

Base: 96.36% // Head: 96.41% // Increases project coverage by +0.05% :tada:

Coverage data is based on head (eb22d9e) compared to base (eab6e2c). Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4186      +/-   ##
==========================================
+ Coverage   96.36%   96.41%   +0.05%     
==========================================
  Files          45       62      +17     
  Lines        2281     2734     +453     
  Branches      640      789     +149     
==========================================
+ Hits         2198     2636     +438     
- Misses         80       96      +16     
+ Partials        3        2       -1     

Impacted Files	Coverage Δ
src/react/useMutation.ts
src/react/utils.ts
...rc/createWebStoragePersistor-experimental/index.ts
src/core/infiniteQueryBehavior.ts
src/devtools/theme.tsx
src/react/useIsMutating.ts
src/core/notifyManager.ts
src/react/useInfiniteQuery.ts
src/devtools/Explorer.tsx
src/react/reactBatchedUpdates.ts
... and 97 more

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