docs: Fix a few typos

[timgates42]

There are small typos in:

• docs/index.rst
• docxtpl/main.py
• docxtpl/template.py
• tests/embedded.py

Fixes:

• Should read surrounding rather than surronding.
• Should read rendering rather than rendring.
• Should read providing rather than provinding.
• Should read optionally rather than optionnally.
• Should read optional rather than optionnal.
• Should read necessary rather than neccessary.
• Should read existing rather than exsting.
• Should read embedded rather than embdded.
• Should read dictionaries rather than dictionnaries.
• Should read cleaning rather than cleanning.
• Should read catches rather than cacthes.

Semi-automated pull request generated by https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md