Update README.md

Clarified one step.

Author: JuliaMongo

tools/license-tool/README.md

@@ -5,7 +5,7 @@ Install [Rust](https://www.rust-lang.org/learn/get-started).
 # Instructions
 
 1) Download the license file for the desired version (for example, https://github.com/10gen/ops-manager-kubernetes/blob/1.19.1/licenses.csv).
-2) Place the licenses.csv file in `/docs-k8s-operator/tools/license-tool/΄`.
+2) Place the licenses.csv file in `/docs-k8s-operator/tools/license-tool/΄`. Check that this directory contains just one such file and remove the previous version of this file if needed.
 3) Change to the tool directory: `cd tools/license-tool/`.
 4) Run the tool: `cargo run`.
 5) Paste the output into the docs at `source/third-party-licenses.txt`.