docs(readme): address review feedback on Task 1 marker widening

- Block C (First run): add "### After PyPI publishing" heading
  wrapped in its own marker pair, mirroring Block B's pattern, so
  today's pre-cleanup reader has a clear signal distinguishing the
  GitHub-source fence from the post-PyPI canonical fence.
- Block E (Diagnostics): add post-cleanup-only intro sentences
  ("Check the local environment:" / "Validate an existing index:")
  outside each marker pair, so the post-cleanup README has proper
  section openings matching the rest of the doc.

Addresses Important #1 and #2 from the code-quality review of
commit 999e219.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ayhammouda

README.md

@@ -124,6 +124,10 @@ uvx --from git+https://github.com/ayhammouda/python-docs-mcp-server.git python-d
 After PyPI publishing, `uvx python-docs-mcp-server build-index ...` is enough.
 <!-- /PRE-PYPI -->
 
+<!-- PRE-PYPI: after the first PyPI publish, drop this "After PyPI publishing" heading so the section reads simply as "## First run" -->
+### After PyPI publishing
+<!-- /PRE-PYPI -->
+
 ```bash
 uvx python-docs-mcp-server build-index --versions 3.10,3.11,3.12,3.13,3.14
 ```
@@ -329,6 +333,8 @@ uvx --from git+https://github.com/ayhammouda/python-docs-mcp-server.git python-d
 After PyPI publishing:
 <!-- /PRE-PYPI -->
 
+Check the local environment:
+
 ```bash
 uvx python-docs-mcp-server doctor
 ```
@@ -348,6 +354,8 @@ uvx --from git+https://github.com/ayhammouda/python-docs-mcp-server.git python-d
 After PyPI publishing:
 <!-- /PRE-PYPI -->
 
+Validate an existing index:
+
 ```bash
 uvx python-docs-mcp-server validate-corpus
 ```