Some docs update

[ydcjeff]

What does this PR do?

• some docs update
• uses tip block
• updates new-project, introduction_guide, converting, performance

Related: #3756

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[codecov]

Codecov Report

Merging #3794 into master will increase coverage by 1%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #3794    +/-   ##
=======================================
+ Coverage      85%     86%    +1%     
=======================================
  Files         110     112     +2     
  Lines        8537    9067   +530     
=======================================
+ Hits         7293    7829   +536     
+ Misses       1244    1238     -6     

[Borda]

@ydcjeff does the "[CI SKIP]" do something?

[ydcjeff]

@ydcjeff does the "[CI SKIP]" do something?

It skips Drone since this is a docs update PR and no doctest in Drone (I think). So, I don't think GPU testing is necessary.
But if we want to test in Drone, feel free to edit.

[Borda]

@ydcjeff does the "[CI SKIP]" do something?

It skips Drone since this is a docs update PR and no doctest in Drone (I think). So, I don't think GPU testing is necessary.
But if we want to test in Drone, feel free to edit.

well then it is tricky since we do not have it in mandatory checks... so it will appear as all green even the GPU and allow merge as the test is skipped... I would not say this much loudly... :D

[Borda]

lgtm

[ydcjeff]

@ydcjeff does the "[CI SKIP]" do something?

It skips Drone since this is a docs update PR and no doctest in Drone (I think). So, I don't think GPU testing is necessary.
But if we want to test in Drone, feel free to edit.

well then it is tricky since we do not have it in mandatory checks... so it will appear as all green even the GPU and allow merge as the test is skipped... I would not say this much loudly... :D

Alright, I will be careful next time.

[awaelchli]

I have to admit I am quite perplexed by some of these docs.
Thanks for proof reading them @ydcjeff

[awaelchli]

Suggested change

	Don't call ``.item()`` anywhere on your code. Use ``.detach()`` instead to remove the connected graph calls. Lightning
	Don't call ``.item()`` anywhere in your code. Use ``.detach()`` instead to remove the connected graph calls. Lightning

This advice of not calling item ANYWHERE in your code is a bit strange. I think everyone who used PyTorch a little bit knows what .item does and when not to use it. This has nothing todo with Lightning. I think mentioning these things like .detach in this introduction is just confusing, and it has nothing todo with Lightning.

Also, what does "Lightning takes a great deal of care to be optimized for this" mean?

[ydcjeff]

It maybe wants to say Lightning has already called .item when needed and not called when unneeded, I think?