add README containing API documentation to project

README.md

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+# Secure User Property Store for RTC
+
+> TODO: introduction, make a cross reference to git commit picker
+
+## Setup Instructions
+The most convenient way to install this service is to download the current stable release from the [Releases](https://github.com/jazz-community/rtc-secure-user-property-store/releases) page.
+
+> TODO: installation and Advanced Properties Configuration instructions
+
+## API Reference
+This section contains the API definition for this project. While we try to do our best to keep this accurate, it is always best to have a look at the code in order to make sure that everything is covered.
+
+### base path
+You'll see the term `<root>` within the following API doc a few times. It represents the root (or base) path for this service. Assuming that your CCM server is being referred to as `localhost:7443/ccm`, the `<root>` path for this service is the following:
+
+> https://localhost:7443/ccm/service/com.siemens.bt.jazz.services.PersonalTokenService.IPersonalTokenService
+
+### Store new Token to Store
+This will add a new entry for the currently logged-in user to the token store. <br>
+The implementing application must somehow remember the `key` of a user as it is required to get the `token` of the user.
+
+**Request URL**
+> POST <root>/tokenStore
+
+**Example Request Body**
+```
+{
+	"key": "gitlab.com",
+    "token": "<this is my secure github accees token>"
+}
+```
+
+**Response Status Code**
+| HTTP Status Code  | When |
+| 201               | The token was successfully added to the database |
+| 400               | Bad Request. Your request must have a body like the one described in _Example Request_. Make sure that it is sent along the network as `application/json` |
+| 401               | The user is not authenticated with RTC Jazz |
+| 500               | An internal server error has occured. Review the CCM log file to find more information | 
+
+### Read token from Store
+Read the token associated to the passed in `key` for the currently logged-in user.
+
+**Request URL**
+> GET <root>/tokenStore?key=`key`
+
+**Response Status Code**
+| HTTP Status Code  | When |
+| 200               | Found the token associated to the passed in `key`, the value is availabe in the response body (see below) |
+| 401               | The user is not authenticated with RTC Jazz |
+| 404               | The currently logged-in user has no token stored yet for the passed in `key`
+| 500               | An internal server error has occured. Review the CCM log file to find more information | 
+
+**Response Body**
+```
+{
+    "token": "<this is my secure github accees token>"
+}
+```
+
+## Contributing
+Please use the [Issue Tracker](https://github.com/jazz-community/rtc-secure-user-property-store/issues) of this repository to report issues or suggest enhancements.<br>
+Pull requests are very welcome.
+
+## Licensing
+Copyright (c) Siemens AG. All rights reserved.<br>
+Licensed under the [MIT](LICENSE) License.