Proposing a PR to fix a few small typos

[timgates42]

Issue Type

[x] Bug (Typo)

Steps to Replicate and Expected Behaviour

• Examine README.md and observe substracted, however expect to see subtracted.
• Examine README.md, pykov.py and observe precedessors, however expect to see predecessors.
• Examine pykov.py and observe coloum, however expect to see column.

Notes

Semi-automated issue generated by
https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

To avoid wasting CI processing resources a branch with the fix has been
prepared but a pull request has not yet been created. A pull request fixing
the issue can be prepared from the link below, feel free to create it or
request @timgates42 create the PR. Alternatively if the fix is undesired please
close the issue with a small comment about the reasoning.

https://github.com/timgates42/Pykov/pull/new/bugfix_typos

Thanks.