[MRG] debug documentation search

[rflamary]

Types of changes

fix doc search with trick from:
readthedocs/sphinx_rtd_theme#1452

Motivation and context / Related issue

How has this been tested (if it applies)

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[codecov]

Codecov Report

Merging #453 (0802d87) into master (89f1613) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #453   +/-   ##
=======================================
  Coverage   94.92%   94.92%           
=======================================
  Files          31       31           
  Lines        6879     6879           
=======================================
  Hits         6530     6530           
  Misses        349      349