NO-JIRA: Fix and improve docs regarding libuv usage

[Jmennius]

CMake variable names are case-sensitive and so -Dproactor doesn't work, fix that.

Also, rephrase the section a bit and mention packages required for libuv usage.

[codecov-commenter]

Codecov Report

Merging #363 (c100bf3) into main (a920192) will increase coverage by 20.11%.
The diff coverage is n/a.

❗ Current head c100bf3 differs from pull request most recent head 0b81afb. Consider uploading reports for the commit 0b81afb to get more accurate results

@@             Coverage Diff             @@
##             main     #363       +/-   ##
===========================================
+ Coverage   68.24%   88.36%   +20.11%     
===========================================
  Files         367       47      -320     
  Lines       73285     2397    -70888     
===========================================
- Hits        50011     2118    -47893     
+ Misses      23274      279    -22995     

Impacted Files	Coverage Δ
cpp/examples/direct_recv.cpp
cpp/src/reconnect_test.cpp
cpp/src/uuid.cpp
cpp/src/tracker.cpp
cpp/examples/simple_recv.cpp
cpp/src/value.cpp
cpp/src/connection_driver_test.cpp
cpp/examples/ssl.cpp
python/tests/proton_tests/handler.py
cpp/src/proactor_container_impl.cpp
... and 310 more

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