Readme update - Githubissues

Description

This PR slightly updates the repo's main readme:

Update and move third party dependencies to a separate readme (we had some missing, and some no-longer used were still referenced)
Add iOS as supported platform (we added support for it some time ago, but didn't update the readme)
Slightly adjust linkage, so that the readme shown on github links to the docs site (doesn't affect Antora builds).

Note: Pure documentation fix

Please ensure the following points are checked:

[x] My code follows the coding style
[x] I have reviewed file licenses
[x] I have commented any added functions (in line with Doxygen)
[x] I have commented any code that could be hard to understand
[x] My changes do not add any new compiler warnings
[x] My changes do not add any new validation layer errors or warnings
[x] I have used existing framework/helper functions where possible
[x] My changes do not add any regressions
[x] I have tested every sample to ensure everything runs correctly
[x] This PR describes the scope and expected impact of the changes I am making

Note: The Samples CI runs a number of checks including:
- [x] I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)
- [x] My changes build on Windows, Linux, macOS and Android. Otherwise I have documented any exceptions