Add notice about torque_control beta status

Author: urfeex

README.md

@@ -8,6 +8,27 @@ The library has no external dependencies besides the standard C++ libraries such
 to make it easy to integrate and maintain. It also serves as the foundation for the ROS and ROS 2
 drivers.
 
+---
+
+> [!IMPORTANT]
+> The **torque_control** branch is a **beta feature**. At the current time, you will need to
+> participate in the public beta program at
+> [https://ur.centercode.com/key/PolyScope5Beta](https://ur.centercode.com/key/PolyScope5Beta) to
+> use it. It will not work with any released robot software version. At a later time this will
+> require a certain robot software version to work and the new features will not work with older
+> software versions. However, old functionality will still be working with older robot software as
+> noted in the version requirements below.
+>
+> This being a beta feature, the API is not to be considered stable. Anything developed on this
+> branch might be changing in a breaking way until it is merged into the master branch.
+>
+> Also, please keep the beta status in mind when operating the robot. Parts of the software
+> involved in the beta-feature might not be tested to the usual extent and might show unexpected
+> behavior in edge cases.
+>
+> Documentation for the new features may also be missing initially. This will be added before
+> merging things to the master branch.
+
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   <img src="doc/resources/family_photo.png" alt="Universal Robot family" style="width: 90%;"/>