* Remove unnecessary screenshot. It doesn't help very much in this
case.
* Update text to instruct users to not leave the `Title` field
empty (it cannot be blank).
* Replace wording such as `Go to Settings` with `Click on Settings`.
* Combine the "fill out the form" and "click 'Save'" steps.
* Replace "Choose X on the left-hand side" with "Choose X".
* Replace "Remember to check the X" with "Check the X".
The change to `render_markdown_path` in `app_filters.py` was
required because for bitbucket2, `integrations.name` is
`bitbucket2`, which is substituted for the stream name in our
Markdown macros. It didn't make sense to recommend the name
`bitbucket2` as a default stream name to our users (for them,
it's just bitbucket). However, the URL is still
`api/v1/external/bitbucket2`.