Fix typos and grammar in docu

[svengoldberg]

Some fixes regarding spelling and grammar in the documentation.
Of course, this is fully open to discussion...

Also, I removed the part about the Android version of TiGL as it is no longer supported.

Fixes #1200.

Checklist:

Task	Finished	Reviewer Approved
At least one test for the new functionality was added.	yes does not apply	OK
New classes have been added to the Python interface.	yes does not apply	OK
The code is properly documented with doxygen docstrings	yes does not apply	OK
Changes are documented at the top of ChangeLog.md	yes does not apply	OK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.97%. Comparing base (33f3df7) to head (b07bed6).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1201   +/-   ##
=======================================
  Coverage   71.97%   71.97%           
=======================================
  Files         308      308           
  Lines       29543    29543           
=======================================
  Hits        21263    21263           
  Misses       8280     8280           

Flag	Coverage Δ
unittests	71.97% <ø> (ø)

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