Fix typos in user guide

[weibeld]

Encountered some typos in the user guide, including a wrong command, which might be confusing otherwise.

[codecov-io]

Codecov Report

Merging #153 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #153   +/-   ##
=======================================
  Coverage   50.91%   50.91%           
=======================================
  Files          13       13           
  Lines         711      711           
=======================================
  Hits          362      362           
  Misses        297      297           
  Partials       52       52

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[ahmetb]

Thanks!