📚 add documentation

docs/Twingle_Project.md

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+# Twingle Project
+
+This campaign type represents Twingle donation forms. *Twingle Projects* are campaigns which get synchronized between
+Twingle and your CiviCRM instance in both directions. A *Twingle Project* has three extra sections:
+
+## Twingle Information
+
+This section shows the external Twingle id, the identifier and the project type (default, event or membership). You can
+change the project type at any time, but please be aware that your Twingle donation forms will change their appearance
+depending on what project type is selevted.
+
+## Twingle Settings
+
+Here you can find almost all settings to configure a donation form. Each setting has a help text.
+
+Currently, there is no front end input validation but all settings get validated on server side when the form gets
+saved. If the validation fails, an error message will be displayed that contains further information. In this case, the
+form won't get saved.
+
+## Twingle Payment Methods
+
+These settings allow you to specify the payment methods that you want to offer to users for one time and recurring
+donations.
+
+Currently, the extension only supports to configure *PayPal*, *bank transfer*, *debit* and *Sofortüberweisung* as one
+time payment methods and *PayPal* and *debit* as recurring payment methods. This may be enhanced in future versions.
+Nevertheless, you can configure additional payment methods in the *[TwingleMANAGER](https://twinglemanager.de)* – they
+won't get overwritten by the *Twingle Campaign* extension.
+
+Please make sure to establish all payment methods in your general *[TwingleMANAGER](https://twinglemanager.de)* settings
+before you try to configure them for *Twingle Projects*.
+
+## Twingle Project Preview
+![TwingleProject](../images/TwingleProject_settings.png)