intro: add note on IPFS usage

how_to_eurec4a/intro.md

@@ -16,6 +16,15 @@ pip install eurec4a[data]
 afterwards, you should have everything installed to access the data. For some examples, you may have to install additional libraries for some specialized plotting methods.
 If you are looking for detailed instructions to set up the entire book project including all dependencies, please refer to {doc}`running_locally`.
 
+```{admonition} use of IPFS
+:class: tip
+We use [IPFS](https://ipfs.tech) to access data in a reliable way.
+In principle, this works with or without a local IPFS node (e.g. [Desktop](https://docs.ipfs.tech/install/ipfs-desktop/) or [CLI](https://docs.ipfs.tech/install/command-line/)).
+We recommend to **run a local node**: this will result in data access performance generally better than more classical ways of access (e.g. OPeNDAP, HTTP), whereas without a local node, access performance can be really poor.
+
+See {doc}`data_on_ipfs` for details on this topic, and options to bypass IPFS.
+```
+
 If you want to give the chapters a really quick try and don't want to set up anything yourself, you'll find a rocket icon (<i class="fas fa-rocket"></i>) in the top bar to the right of each chapter. The icon provides two interactive ways to run the code: `Binder` and `LiveCode`. In both cases a virtual environment is created for you in the background by a click on the respective link and you don't have to take care of any requirements locally on your machine.
 
 In principle, we anticipate to have at minimum one example script per instrument and we are very happy about contributions by you :)