Signify 'devcontainer.json' through backticks

[hsnabszhdn]

Applying the guidelines as per contributing.md:

Signify devcontainer.json is a file type through backticks

Once wrapped with backticks, the articles should follow these rules:

Articles not needed:

• Add thisProp to devcontainer.json
• Use thisProp in devcontainer.json

Articles needed (the article refers to file, not to devcontainer.json):

• Add a new devcontainer.json file to your repo
• Add thisProp to the devcontainer.json file