Fix typos in documentation

[pratikmota]

Description

Motivation:
Improving FerretDB documentation.
Changes:
Adding typo correction in the documentation.

1. reference (glossary.md)
   Current: processsing , New change: processing

2. basic-operation (read.md)
   Current: retrieveing, New change: retrieving

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.

[CLAassistant]

All committers have signed the CLA.

[AlekSi]

Thank you!

[codecov]

Codecov Report

Merging #3217 (7aeb9fb) into main (76e3b2e) will decrease coverage by 2.99%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3217      +/-   ##
==========================================
- Coverage   74.99%   72.00%   -2.99%     
==========================================
  Files         396      396              
  Lines       22210    22210              
==========================================
- Hits        16656    15993     -663     
- Misses       4561     5171     +610     
- Partials      993     1046      +53     

see 70 files with indirect coverage changes

Flag	Coverage Δ
hana	?
integration	68.04% <ø> (-3.32%)	⬇️
mongodb	5.30% <ø> (ø)
pg	60.40% <ø> (-4.80%)	⬇️
shard-1	56.63% <ø> (+0.15%)	⬆️
shard-2	27.80% <ø> (-24.48%)	⬇️
shard-3	55.77% <ø> (+0.56%)	⬆️
sqlite	38.58% <ø> (+6.77%)	⬆️
unit	24.64% <ø> (-0.03%)	⬇️

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