Updated main index.rst as well as created nested User Guide table of content with necessary subsections

[MustafaAbdaal]

Motivate of the pull request

• To address an existing issue. If so, please provide a link to the issue:
• Breaking new feature. If so, please describe details in the description part.

Describe the technical details

What is currently done? (Provide issue link if applicable)

What does this pull request change?

modified main index.rst, added user_guide section, created section files (Intro, Setting up Project, FPGA input, SoC, input, Memory, Peripherals & Results) & lastly added subsection headings. User Guide's preliminary Table of Contents is created, it is separate from rest of the readthedocs content in to make it easier to modify.

Which part of the code base require a change

• Frontend:
• Backend:
• Library: <Specify the library name, e.g. npm packages>
• Plug-in: <Specify the plugin name, e.g. Webpack, jtest>
• Documentation
• Regression tests
• Continuous Integration (CI) scripts

Impact of the pull request

• Require a change on Quality of Results (QoR)
• Break backward-compatibility. If so, please list who may be influenced.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.83%. Comparing base (03e2e77) to head (8dfe5d8).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #256   +/-   ##
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  Coverage   68.83%   68.83%           
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  Files         110      110           
  Lines        9022     9022           
  Branches      402      402           
=======================================
  Hits         6210     6210           
  Misses       2812     2812           

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