documentation:introduction: fix typos and grammar

[Quin-Darcy]

This pull request focuses on correcting spelling and grammatical errors in the Documentation/teaching/labs/introduction.rst file. These changes improve the clarity and professionalism of the documentation.

Spelling Corrections:

• Corrected "mantained" to "maintained" in the description of Kscope.
• Fixed "efectively" to "effectively" in the explanation of SourceWeb indexing.
• Changed "stduent" to "student" in a gdb session example.
• Updated "bellow" to "below" in the section on Linux kernel advantages.
• Replaced "exercice" with "exercise" in the remarks section.

Minor Text Adjustments:

• Improved phrasing by removing redundant words in the explanation of LXR usage.
• Corrected "filed" to "file" when describing the output of the btrace.log process.
• Fixed a typo in "gaining documenting" to "gaining documentation" in the lab objectives.