fix #1167: Added installation.rst to docs

[DON-BRAN]

[Description of PR]

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[joshmoore]

Looking at https://zarr--1170.org.readthedocs.build/en/1170/index.html, I'd suggest removing from the main page since now it's listed twice.

[codecov]

Codecov Report

Merging #1170 (e013e1a) into main (53357f7) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1170      +/-   ##
==========================================
- Coverage   99.95%   99.95%   -0.01%     
==========================================
  Files          36       36              
  Lines       14143    14142       -1     
==========================================
- Hits        14136    14135       -1     
  Misses          7        7              

Impacted Files	Coverage Δ
zarr/util.py	100.00% <0.00%> (ø)

[joshmoore]

Thanks again, @DON-BRAN. 👍