Documentation: Improvements to "Reading NWB Files" section

[ehennestad]

Motivation

Improve documentation:

• Add missing function and class references for nwbRead / NwbFile
• Update information box on lazy reading in "Reading NWB Files" section to focus more on files
• Improve explanation sections for DataStubs and DataPipes

Link to docs

How to test the behavior?

N/A

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.59%. Comparing base (6cb513a) to head (e11b3f8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #769   +/-   ##
=======================================
  Coverage   95.59%   95.59%           
=======================================
  Files         184      184           
  Lines        6443     6443           
=======================================
  Hits         6159     6159           
  Misses        284      284           

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