[Docs] Update tutorial links in readme

[tcbegley]

Description

Correct links to tutorials in README.

Closes #723

[codecov]

Codecov Report

Merging #724 (b0d9b2d) into main (08e3b71) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #724   +/-   ##
=======================================
  Coverage   88.66%   88.66%           
=======================================
  Files         120      120           
  Lines       20186    20186           
=======================================
+ Hits        17897    17898    +1     
+ Misses       2289     2288    -1     

Flag	Coverage Δ
habitat-gpu	25.05% <ø> (ø)
linux-cpu	85.59% <ø> (ø)
linux-gpu	86.54% <ø> (ø)
linux-jumanji	30.27% <ø> (ø)
linux-outdeps-gpu	72.22% <ø> (ø)
linux-stable-cpu	85.44% <ø> (ø)
linux-stable-gpu	86.18% <ø> (+0.01%)	⬆️
linux_examples-gpu	43.09% <ø> (ø)
macos-cpu	85.26% <ø> (-0.01%)	⬇️
olddeps-gpu	76.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
test/test_trainer.py	98.23% <0.00%> (-0.33%)	⬇️
torchrl/envs/vec_env.py	69.06% <0.00%> (+0.50%)	⬆️

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[vmoens]

LGTM thanks!