Add SQLite set up docs

[Fashander]

Description

Closes #3369.

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Milestone (Next), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #3568 (6c50af7) into main (e82aefb) will decrease coverage by 0.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3568      +/-   ##
==========================================
- Coverage   61.82%   61.45%   -0.38%     
==========================================
  Files         426      426              
  Lines       27584    27584              
==========================================
- Hits        17054    16951     -103     
- Misses       9523     9608      +85     
- Partials     1007     1025      +18     

see 13 files with indirect coverage changes

Flag	Coverage Δ
filter-true	57.92% <ø> (-0.46%)	⬇️
hana-1	3.01% <ø> (ø)
integration	57.92% <ø> (-0.46%)	⬇️
mongodb-1	4.49% <ø> (ø)
postgresql-1	42.47% <ø> (ø)
postgresql-2	39.85% <ø> (ø)
postgresql-3	41.92% <ø> (-0.02%)	⬇️
sort-false	57.92% <ø> (-0.46%)	⬇️
sqlite-1	42.27% <ø> (ø)
sqlite-2	?
sqlite-3	?
unit	22.69% <ø> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[noisersup]

The #3571 is merged, we're ready to remove the variable, apart from that LGTM

[noisersup]

Looks good to me!

[chilagrow]

🚀