Add hint to README to fix an error with building a Docker image

[j-eissler]

This is just a small commit that should help people trying to build their own Docker image. When running the build command from the readme file the error failed to solve: error from sender: context canceled can occur. This can easily be fixed by making sure the Eclipse IDE isn't open. To avoid others having to search for a solution I would like to add this info to the readme.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Additional details and impacted files

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+ Coverage      55.91%   56.01%   +0.11%     
- Complexity      8052     8197     +145     
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  Lines          87955    89017    +1062     
  Branches        6502     6560      +58     
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+ Hits           49170    49853     +683     
- Misses         37094    37446     +352     
- Partials        1691     1718      +27     

[da-Kai]

@j-eissler
Thank you for your contribution! There are a few improvements I'd suggest to make it more comprehensive:

1. It would be great to move this content to the end of the README under a new section titled # Common Problems and Solutions.

2. The same topic should also be included in the backend Docker README, as it's relevant there too.
   tools/docker/backend/README.md

3. The issue you're describing isn't exclusive to Eclipse IDE. It can occur with any program that locks files. Could you please adjust the wording to something like: "Ensure no program is accessing the files", and use Eclipse IDE as an example?

[j-eissler]

@da-Kai Thanks for the feedback! I've updated the description according to your response.