[Umka/en] add a page for Umka

[marekmaskarinec]

• I solemnly swear that this is all original content of which I am the original author
• Pull request title is prepended with [language/lang-code] (example [python/fr-fr] or [java/en])
• Pull request touches only one file (or a set of logically related files with similar changes made)
• Content changes are aimed at intermediate to experienced programmers (this is a poor format for explaining fundamental programming concepts)
• If you've changed any part of the YAML Frontmatter, make sure it is formatted according to CONTRIBUTING.md
  • Yes, I have double-checked quotes and field names!

[vendethiel]

Sorry, these links look broken now. Do you mind updating them?

[vendethiel]

Thanks for your contribution, sorry for the delay.

[marekmaskarinec]

I will do more changes to the document. Many things changed in umka since I wrote it.

[vendethiel]

Thank you very much!

[marekmaskarinec]

@verhovsky thanks for the fixes, but I still have to make some changes to the document since the language changed a bit in the past two years. It should be done by the end of the weekend.

[verhovsky]

@marekmaskarinec ping

[marekmaskarinec]

Oops, sorry. I will put it on my calendar.