Add story about updating account details.

docs/update-account-details.mdown

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+# Update account details
+
+When I click an icon/symbol/link (something like a setting symbol or account symbol) I am taken to a page where I can update my account's settings.
+
+_Account settings include:_
+
+- Username *
+- E-mail address *
+- Account password *
+
+_* => fields are deemed 'critical'._
+
+## Acceptance tests
+
+- When on my account details page, I see a form where I can update all fields.
+- When updating critical details (atm. all details are critical) I need to confirm my identity by entering my current password.
+- When updating my password, I need to write the password twice to confirm that I wrote it correctly (two different fields).
+- When working with passwords, the characters I enter in a password field are obscured.
+
+### Danger Zone
+
+- There is a secluded area called the _'Danger Zone'_ where irreversable account actions are handled.
+- In the danger zone, I can push a button to delete my account. If I push this button I should be prombted by a confirmation prompt asking if I really want to delete my account. If I confirm, the account should be flagged (which is another story).