Add Emscripten Build Instructions

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

This PR will add instructions on how to build a wasm version of CppInterOp and xeus-cpp.

Fixes # (issue)

Type of change

Please tick all options which are relevant.

• Bug fix
• New feature
• Requires documentation updates

Testing

Please describe the test(s) that you added and ran to verify your changes.

Checklist

• I have read the contribution guide recently

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.84%. Comparing base (4959cce) to head (0783abf).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #390      +/-   ##
==========================================
+ Coverage   70.62%   70.84%   +0.21%     
==========================================
  Files           9        9              
  Lines        3500     3529      +29     
==========================================
+ Hits         2472     2500      +28     
- Misses       1028     1029       +1     

see 2 files with indirect coverage changes

see 2 files with indirect coverage changes

[anutosh491]

Overall formatting looks a bit weird, I don't know why that happens but everything seems left aligned.
Can't we have the docs to fit the page ?

[mcbarton]

@anutosh491 I am aware if the weird formatting and will fix before it gets merged when we are happy with the contents

[anutosh491]

I shall review this soon !

[anutosh491]

Merging this with the xeus-cpp changes doesn't make sense as this won't work already. Maybe let's keep this PR to getting an emscripten build for cppinterop ?

Once I raise a PR on xeus-cpp to get xeus-cpp-lite and that goes in I shall change the readme's in both xeus-cpp and cppinterop on how to get xeus-cpp-lite ?

[mcbarton]

@anutosh491 I'll wait until you make the change to get xeus-cpp-lite working. I'll change accordingly if necessary.

[anutosh491]

xeus-cpp-lite build instructions need to be edited but otherwise looks good. Merging after CI passes.