Fix tutorial typos and improve styling

[alejandromumo]

Fixed typos in tutorial's README.

Improved styling following markdown linting rules using markdownlint, as suggested in #83 . Namely:

• Fixed indentation for code blocks and text inside a list's item. Apart from being unsightly in the rendered markdown, also triggered linting's rule md029.
• Fixed commandline vs bash vs console inconsistencies in code-blocks containing shell commands. For instance:
  • Replaced commandline with console whenever the written command contains prompts. E.g:

    john@doe:~$ ls -la
    foo bar

    Instead, if using bash it would render as:

    john@doe:~$ ls -la
    foo bar

    Otherwise, bash can be used.
  • bash with or without $. Added $ before a command with output, removed it otherwise following linting rule md014.
• Fixed trailing spaces md009 and EOF spaces md047
• Fixed blank lines surrounding headers, following rule md022

[avivace]

Thanks @alejandromumo ! I left some comments, but it looks good so far. Can you rebase the branch so it has only one / meaningful commits?

[avivace]

Here are you replacing the bash syntax highlighting with console but in other occurences the other way round? (e.g. in 13-securing-your-instance/README.md?)

[alejandromumo]

console can be used when a command has prompt. In this case, (my-site) $ invenio webpack buildall contains a prompt. That way, prompt is properly styled when rendered.
bash can be used otherwise, as in https://github.com/inveniosoftware/training/pull/111/files#diff-40659415052de7162a64a8e03acc79f60e6592424c71a8826849917684e1380f where command does not contain any prompt.

[avivace]

If we decide to remove every $ character to make the strings copy-pastable maybe we should to the same with the virtual env prompts (if no additional clarificaiton on it being used is required)

[alejandromumo]

I don't have any objection to that.
But these prompts provide a hint to the reader that the command was run in a specific venv. Otherwise the command should be modified as well (e.g. in this case pipenv run pip install Pillow)