Improve release documentation

[ArkaSaha30]

This commit will improve the release documentation guide by incorporating the following points:

1. Step 5 can be simplified to do a single-branch checkout
2. Step 6 should clarify that the release directory is in /tmp/etcd-release-${VERSION}/etcd/release/
3. Step 8 mention to add the "Release" label to the announcement message

Reference: #18485 (comment)

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.85%. Comparing base (4997a2b) to head (242cb5b).

❗ Current head 242cb5b differs from pull request most recent head 00f8a47

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Additional details and impacted files

see 12 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #18572      +/-   ##
==========================================
- Coverage   68.89%   68.85%   -0.04%     
==========================================
  Files         420      420              
  Lines       35474    35474              
==========================================
- Hits        24439    24426      -13     
- Misses       9621     9631      +10     
- Partials     1414     1417       +3     

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[jmhbnz]

LGTM - Thanks for helping make the next release better @ArkaSaha30 :)

[ivanvc]

LGTM. Thanks, @ArkaSaha30.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, ArkaSaha30, ivanvc, jmhbnz

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