Update README.md

[sbuis]

• review README.md
• document cropr_simulation format (for sim and obs)
• Hide code about stics (get_sim...)
• remove unecessary references to STICS
• remove intercrop in examples when possible
• see if new examples should be added
• update badges

[sbuis]

There is a problem in section 2.1.3
Scatter plot is not correct due to bad shape of sim2.
names(sim2) gives [1] "IC_Wheat_Pea_2005-2006_N0" NA

This does not happen with SticsRFiles release 1.6.0.
This happens with SticsRFiles main (e.g. after 363c49460698b1df7aaaabd1e2e7c3531e62cac8).
Opened issue SticsRPacks/SticsRFiles#228