Update and reorganize README.md

[odow]

x-ref https://github.com/jump-dev/JuMP.jl/pull/3624

I've made quite a few changes, so it's probably best viewed https://github.com/odow/Optim.jl/blob/patch-1/README.md

Main changes are:

• Remove table of badges
• Use explicit Markdown links
• Remove mathematical description of rosebbrock
• Remove suggestion to tag @pfkod explicitly
• Fix JuMP example, which @blegat got wrong 😆 (missing objective sense)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (ca3513f) 84.97% compared to head (c2f7cd6) 84.85%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1076 +/- ## ========================================== - Coverage 84.97% 84.85% -0.12% ========================================== Files 46 46 Lines 3480 3480 ========================================== - Hits 2957 2953 -4 - Misses 523 527 +4 ```

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[odow]

Will look like https://jump.dev/JuMP.jl/previews/PR3624/packages/Optim/

[pkofod]

Looks good. I did suggest a change, because the slack channel name has math- first

[odow]

Done.

[pkofod]

Thanks