Update tutorials.rst

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Update table_of_content_introduction.rst
ability to compile for iOS with Neon
Implementation detector and selector for IPP and OpenCL;

IPP can be switched on and off on runtime;

Optional implementation collector was added (switched off by default in CMake). Gathers data of implementation used in functions and report this info through performance TS;

TS modifications for implementations control;
Merge pull request #3335 from ilya-lavrenov:neon_ios
Merge pull request #3333 from micha137:patch-1
Merge pull request #3334 from micha137:patch-2
Applied proposed fix
fixes
Merge pull request #3270 from boaz001:patch-1
Merge pull request #3338 from ilya-lavrenov:ios_fixes
Merge pull request #3332 from lupustr3:pvlasov/implementation_detector