[Example] Add microstates analysis example

[anshu-97]

Description

This PR aims at adding a simple example to demonatrate how nk functions can be used to extract microstates and conduct basic microstate analysis

Proposed Changes

I added an example file in docs > examples > microstates_example

Checklist

Here are some things to check before creating the PR. If you encounter any issues, do let us know :)

• I have read the CONTRIBUTING file.
• My PR is targetted at the dev branch (and not towards the master branch).
• I ran the CODE CHECKS on the files I added or modified and fixed the errors.
• I have added the newly added features to News.rst (if applicable)

[codecov-commenter]

Codecov Report

Base: 53.15% // Head: 53.17% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (212508b) compared to base (d37ca7a).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #739      +/-   ##
==========================================
+ Coverage   53.15%   53.17%   +0.01%     
==========================================
  Files         290      290              
  Lines       12964    12964              
==========================================
+ Hits         6891     6893       +2     
+ Misses       6073     6071       -2     

Impacted Files	Coverage Δ
neurokit2/rsp/rsp_simulate.py	99.10% <0.00%> (+0.89%)	⬆️
neurokit2/eda/eda_eventrelated.py	83.67% <0.00%> (+2.04%)	⬆️

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