config editing through database

docs/admin/config.md

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+# Configuring instance
+You can configure your instance from admin interface. You need account with admin rights and little change in config file, which will allow settings dynamic configuration from database.
+
+```elixir
+config :pleroma, :instance,
+  dynamic_configuration: true
+```
+
+## How it works
+Settings are stored in database and are applied in `runtime` after each change. Most of the settings take effect immediately, except some, which need instance reboot. These settings are needed in `compile time`, that's why settings are duplicated to the file.
+
+File with duplicated settings is located in `config/{env}.exported_from_db.exs`. For prod env it will be `config/prod.exported_from_db.exs`.
+
+## How to set it up
+You need to migrate your existing settings to the database. You can do this with mix task (all config files will remain untouched):
+```bash
+mix pleroma.config migrate_to_db
+```
+Now you can change settings in admin interface. After each save, settings are duplicated to the `config/{env}.exported_from_db.exs` file.
+
+<span style="color:red">**ATTENTION**</span>
+
+**<span style="color:red">Be careful while changing the settings. Every inaccurate configuration change can break the federation or the instance load.</span>**
+
+*Compile time settings, which require instance reboot and can break instance loading:*
+- all settings inside these keys:
+  - `:hackney_pools`
+  - `:chat`
+  - `Pleroma.Web.Endpoint`
+- partially settings inside these keys:
+  - `:seconds_valid` in `Pleroma.Captcha`
+  - `:proxy_remote` in `Pleroma.Upload`
+  - `:upload_limit` in `:instance`
+
+## How to remove it
+
+1. Truncate or delete all values from `config` table
+```sql
+TRUNCATE TABLE config;
+```
+2. Delete `config/{env}.exported_from_db.exs`.
+
+For `prod` env:
+```bash
+cd /opt/pleroma
+cp config/prod.exported_from_db.exs config/exported_from_db.back
+rm -rf config/prod.exported_from_db.exs
+```
+*If you don't want to backup settings, you can skip step with `cp` command.*
+
+3. Set dynamic configuration to `false`.
+```elixir
+config :pleroma, :instance,
+  dynamic_configuration: false
+```
+4. Restart pleroma instance
+```bash
+sudo service pleroma restart
+```