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