DOC:Update python version support info
Updated the python version support info.
Added minimum version for Python 3.5 is 3.5.3 and removed python 2.7 support info.

closes #27558

Looks good to me. Is this the last area that needed to be fixed? We can probably drop the "Plan for dropping Python 2.7" starting on line 20. L932 in user_guide/io.rst also refers to 2.7

```
932:   an ordering on their keys. On Python 2.7+ you may use `collections.OrderedDict`
``` @TomAugspurger so I just have to remove the part on "Plan for dropping Python 2.7" starting on line 20? > @TomAugspurger so I just have to remove the part on "Plan for dropping Python 2.7" starting on line 20?

yes looks ok, the docs checks are failing, click thru to see. ping on green. @jreback I understand the problem. The internal ref, `install.dropping-27`, which was pointing to the section which I just removed on "Droping Python 2.7"  is now broken. There are few instances of this ref in the `doc/source/whatsnew/` files. Should I remove the reference in those files then ? what you need to do is replace the refs with actual http links to the 0.24.2 docs

https://pandas.pydata.org/pandas-docs/version/0.24/install.html#install-dropping-27 Thanks @sameshl, this looks good.

@jreback for doc-only PRs that aren't specific to 0.25, I think we shouldn't backport. What do you think? @TomAugspurger agree generally on this point
however we want this one to update the 0.25.x docs as it’s particularly relevant SGTM.

On Thu, Aug 1, 2019 at 6:44 AM Jeff Reback <notifications@github.com> wrote:

> @TomAugspurger <https://github.com/TomAugspurger> agree generally on this
> point
> however we want this one to update the 0.25.x docs as it’s particularly
> relevant
>
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 thanks @sameshl  Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
$ git checkout 0.25.x
$ git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
$ git cherry-pick -m1 52362bf220d902c87850dde473c1cebc048ee744
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
$ git commit -am 'Backport PR #27580: DOC:Update python version support info'
```

4. Push to a named branch :

```
git push YOURFORK 0.25.x:auto-backport-of-pr-27580-on-0.25.x
```

5. Create a PR against branch 0.25.x, I would have named this PR:

> "Backport PR #27580 on branch 0.25.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 Thanks @jreback and @TomAugspurger!