Add walkthrough to ReadTools documentation pages

[magicDGS]

This requires a small dataset and example code for running ReadTools.

[magicDGS]

@AnnaMariaL suggested to do two sections in the walkthrough:

Standardization

• How to get from everything to STANDARD
• 3 examples with links to downloadable data (see #290) and command-line code. The examples should be common formats: split FASTQ, pair-end BAM with BC/B2 tags, and single-end file (either FASTQ or BAM).
• For other data-format, a table linking parameters and type of data. Example data will be in a different page (see #290).

Processing

• How to process standard format: BAM file already processed.
• Code examples for a common pipeline: de-multiplex and trimming.
• For other data formats, the input parameters should be changed by the correspondence in the linked table mentioned in Standardization.

[magicDGS]

We can also provide argument files for common processing pipelines. For example, for paired-BAM files it will include the --interleavedInput to allow users to re-use it and do not forget to add it (that's one of the most common mistakes when processing BAM files).