Added docstring documentation to SpeakActivity class and poll_accelerometer function

[mebinthattil]

No description provided.

[quozl]

We have hundreds of activities with the activity class not documented in this way, so it doesn't make sense to add this documentation to just one activity. The text doesn't say anything that isn't obvious, almost as if it is automatically generated.

Your text in the accelerometer check makes the assertion that only tablets have accelerometers, and I worked really hard to put an accelerometer in a laptop.

Your commit messages do not follow our guidance.

[mebinthattil]

Noted, shall make future commits accordingly.

[quozl]

You don't need to wait until future commits, you can use git rebase -i to reword these ones and then force push. https://github.com/sugarlabs/sugar-docs/blob/master/src/contributing.md#making-commits is our guidance on wording.