Fix punctuatio

[operatorus]

Several text files have many punctuation errors and other linguistic problems:

• ru/1-1-Approach.md

• ru/1-2-Examples.md

• ru/1-3-Modeling.md

• ru/1-4-Program.md

• ru/1-6-Engineer.md

• ru/1-7-Paradigms.md

I'll try to solve them at least partially.