Write a contributing guide, and fix what the forge move left stale (#96)

(docs) Update all the docs to be up to date with current status quo

.gitea/ISSUE_TEMPLATE/bug_report.md

@@ -1,23 +0,0 @@
----
-name: Bug report
-about: Something doesn't work the way it should
-title: ""
-labels:
-  - bug
----
-
-### What happened
-
-
-### What you expected
-
-
-### Steps to reproduce
-1.
-2.
-3.
-
-### Environment
-- Calendula version: <!-- Settings → bottom of the screen -->
-- Android version:
-- Device:

.gitea/ISSUE_TEMPLATE/crash_report.md

@@ -1,27 +0,0 @@
----
-name: Crash report
-about: Report a crash. Calendula can capture this for you (Settings → Report a problem, or the prompt after a crash) — it copies the report to your clipboard and prefills this form.
-title: "Crash: "
-labels:
-  - bug
-  - crash
-  - priority:high
----
-
-<!--
-Thanks for reporting a crash in Calendula!
-
-If the app prefilled this for you, the crash report is already below — just add
-what you were doing and submit. Otherwise, paste the report from your clipboard
-into the code block. The report contains only app/Android/device versions and the
-stack trace — no personal data or calendar content.
--->
-
-### What happened
-
-
-### Crash report
-
-```
-(paste the crash report here)
-```

.gitea/ISSUE_TEMPLATE/feature_request.md

@@ -1,16 +0,0 @@
----
-name: Feature request
-about: Suggest an idea or improvement
-title: ""
-labels:
-  - feat
----
-
-### What would you like Calendula to do?
-
-
-### Why — what problem does it solve?
-
-
-### Anything else
-<!-- mockups, examples from other apps, alternatives you considered -->

.gitea/ISSUE_TEMPLATE/question.md

@@ -1,19 +0,0 @@
----
-name: Question
-about: Ask how something works or get help using Calendula
-title: ""
-labels:
-  - question
----
-
-### Your question
-
-
-### What you've tried
-<!-- so far, if anything -->
-
-
-### Context
-- Calendula version: <!-- Settings → bottom of the screen -->
-- Android version:
-- Device: