Update README.md and Installation Guide

[mkoeppe]

These need to be updated to reflect the installation changes in 9.1.

As the same time, we do some overdue updates (e.g., remove mention of Solaris) and remove some duplication to simplify maintenance.

Related issues:

• Website updates:

[x] ​https://github.com/sagemath/website/pull/187 - Get rid of links to download-packages.html

• Should remove outdated, duplicated, misleading material at wiki.sagemath.org or mark as outdated:

[x] ​https://wiki.sagemath.org/SupportedPlatforms (marked as outdated)

[dimpase]

I don't like full removal of

-Ports are in progress to some other, less common platforms. The list of
-supported platforms and their current statuses are given in [our wiki](https://wiki.sagemath.org/SupportedPlatforms).
-
-If you are interested in helping port Sage to a new platform, please let
-us know at the [sage-devel mailing list](https://groups.google.com/group/sage-devel)

the last 2 lines ought to stay, IMHO. Wiki may be mentioned with a caveat that that info may be severely outdated.

---

New commits:

​500b74c	README.md: Do not mention Solaris, remove link to outdated wiki
​5832ab0	README.md: Add ./configure to install instructions

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​a23d56e

README.md: Restore mention of porting to other platforms

[mkoeppe]

Replying to dimpase:

the last 2 lines ought to stay, IMHO.

Re-added, re-worded.

Wiki may be mentioned with a caveat that that info may be severely outdated.

It will be easy to add links to up to date information to README if that becomes available.

[mkoeppe]

​https://wiki.sagemath.org/Distribution is one of the few useful wiki pages.

We should link to it from the installation manual, and remove duplication.

[mkoeppe]

By the way, I have prepared ​https://wiki.sagemath.org/ReleaseTours/sage-9.1

[dimpase]

is it still new, or needs review ?

[mkoeppe]

"1. Optional: Read this if you are intending to run a Sage notebook server for multiple users. For security (i.e., to run notebook(secure=True)`) you want to access the server using the HTTPS protocol. First, install OpenSSL and the OpenSSL development"

is this referring to the outdated notebook?

[dimpase]

Replying to mkoeppe:

"1. Optional: Read this if you are intending to run a Sage notebook server for multiple users. For security (i.e., to run notebook(secure=True)`) you want to access the server using the HTTPS protocol. First, install OpenSSL and the OpenSSL development"

is this referring to the outdated notebook?

Oh yes, this should be removed,it's about sagenb

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​b98f7dd

README.md: Do not mention the notebook

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​f7d9b28

README.md: Some updates on 'configure'

[mkoeppe]

I'll stop here but there are obvious ways to improve it even further.

• There should not be both "Quick Instructions" and "More Detailed Instructions" in here. Should be merged & links to install manual added.

[dimpase]

There is some special hell related to OpenSSL on MacOS. Perhaps it should be said in README.

[mkoeppe]

Replying to dimpase:

There is some special hell related to OpenSSL on MacOS. Perhaps it should be said in README.

I think this is not a problem when any system python3 is used.

[dimpase]

please see some fixes here: ​https://gitlab.com/dimpase/sage/-/commit/a6befb26cff1640aee33ed7f27c8a796ee27b85a

[mkoeppe]

All nice. Please push them to the ticket.

For Cygwin, can also refer to the installation manual. There’s a section on Cygwin now

[dimpase]

OK

---

New commits:

​88bb330	README.md updates
​172afc1	some README fixes

[dimpase]

rebased over 9.1.rc0