[BUGFIX] two typos in build instruction doc

[alv67]

Closes #236

📑 Description

✅ Checks

• [x] My pull request adheres to the code style of this project
• [ ] My code requires changes to the documentation
• [x] I have updated the documentation as required
• [x] All the tests have passed

ℹ Additional Information

[gmacario]

@alv67 I am reviewing this PR on a laptop without stud.io CAD, therefore I assume LGTM. Merging PR

[gmacario]

BTW @alv67 are you also planning to release an updated PDF?