Update Caching documentation

[eamanu]

Any headers from serve are ignored. So, this PR remove
the paragraph that mention that. See #8009 and #5670

Close #8009

[eamanu]

I close and reopen the PR because some checks fail.

[eamanu]

ok, errors are repeated

[pradyunsg]

@eamanu could you rebase this on the current master?

[McSinyx]

To quote @uranusjr in another ticket:

Test failures are unrelated, caused by availability issues of http://svn.colorstudy.com.

The whole CI thing doesn't seem to like pip lately 😞

[pradyunsg]

Which ticket? And which test is this?

[McSinyx]

@pradyunsg, it's #8781 (comment). The failures are of tests dealing projects from SVN (which are fetched from the mentioned URL).

[eamanu]

Hi @pradyunsg, the branch is up-to-date with master, thanks

But, like yes @McSinyx seems to be a external error https://github.com/pypa/pip/pull/8780/checks?check_run_id=1001079950

[pradyunsg]

@eamanu master is green -- try now?

[eamanu]

@pradyunsg git rebase run :) thanks!

edit: \o/ green!

[pradyunsg]

Hah! Considering how much effort this PR took, I can only infer that removing lines from a codebase really is very difficult. ;)

[pradyunsg]

Thanks @eamanu! ^>^