Add a README Teads file (prebid#83)

CODEOWNERS

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+* @ebuzzing/ssp

README_TEADS.md

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+# service-prebid
+
+This repository is a copy of [ebuzzing/Prebid.js](https://github.com/ebuzzing/Prebid.js) which is a fork of [prebid/Prebid.js](https://github.com/prebid/Prebid.js)
+
+Here are the main branches :
+
+- **master** --> synchronized with prebid/Prebid.js
+- **master-teads** --> based on master with Teads CI commits
+
+## Contributing
+
+Before contributing, be sure to have the main branches up to date.  
+If it's not the case, ask to ***#ssp-omnichannel-supply-lane*** to update them (only this team have the right to do it)
+
+To update branches :
+
+1. Go to [ebuzzing/Prebid.js](https://github.com/ebuzzing/Prebid.js) and click on `Sync fork` --> This will update the master branch of [ebuzzing/Prebid.js](https://github.com/ebuzzing/Prebid.js)
+
+2. Come back to `service-prebid` and execute these commands on `master` branch
+
+```
+    git remote add upstream https://github.com/ebuzzing/Prebid.js.git # only if you don't have this remote endpoint yet   
+    git fetch upstream  
+    git rebase upstream/master
+    git push origin master --force 
+```
+
+3. Checkout on `master-teads` branch and rebase on `master` then push -force
+
+```
+    git checkout master-teads
+    git rebase master 
+    git push origin master-teads --force
+```
+
+4. Before commit, think to run test and format your code or CI will fail 
+
+```
+    gulp test --fix
+```
+
+## Build
+
+To build only prebid.js file with Teads modules :
+
+    gulp build --modules=userId,consentManagement,teadsIdSystem,teadsBidAdapter
+
+You can add any other modules at the end of the list
+
+## Testing
+
+Example :
+
+    gulp test --nofixlint --file "test/spec/modules/teadsIdSystem_spec.js"
+
+To functionnal test new dev on teadsIdSystem or teadsBidAdapter, please follow this page [How to debug with Charles Proxy](https://teads.atlassian.net/wiki/spaces/SSP/pages/4413590206/Debug+with+Charles)
+