Add concepts directory with power levels guide.

docs/concepts/_category_.json

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+{
+    "label": "Concepts",
+    "position": 2.5,
+    "link": {
+      "type": "generated-index",
+      "description": "Draupnir & Matrix Concepts"
+    }
+  }

docs/concepts/power-levels.md

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+---
+sidebar_position: 0
+sidebar_label: Matrix power levels
+---
+
+<!--
+SPDX-FileCopyrightText: 2022 The Matrix.org Foundation C.I.C.
+SPDX-FileCopyrightText: 2024 Gnuxie <Gnuxie@protonmail.com>
+
+SPDX-License-Identifier: CC-BY-SA-4.0
+
+SPDX-FileAttributionText: <text>
+This modified file contains work from the matrix.org website
+https://github.com/matrix-org/matrix.org
+</text>
+-->
+
+# Matrix power levels
+
+Instead of a system like roles that you may be familiar with, Matrix has a
+system called power levels. A power level is a number that normally ranges
+between 0 to 100[^power-levels-range]. Within a room, each user has a power level
+and each _permission_ also has a power level. For a user to be
+able to use a _permission_, to for example remove a user, they have to have
+the same (or a greater) power level than the power level of the permission.
+
+## Standard roles
+
+By default, Matrix homeservers and clients use different power levels to define
+three roles:
+
+| Power Level | Role          |
+| ----------- | ------------- |
+| 0           | User          |
+| 50          | Moderator     |
+| 100         | Administrator |
+
+With the defaults, each member of a role will be able to do the following:
+
+- **Users** can send messages, media, reactions and redact their own messages in
+  a room.
+- **Moderators** can also change the room name, address, topic, remove users
+  from the room (temporarily or permanently), redact other's messages and send a
+  notification to everyone in the room at once using `@room`.
+- **Administrators** can also change the history visibility (whether people can
+  see messages from before they joined or not), enable encryption in the room,
+  remove entire servers from the room, and promote others to Moderator or
+  Administrator.
+
+Most members of a community are going to be regular users. Usually
+Moderators are appointed to handle ad-hoc moderation issues, for example
+removing or banning spam bots.
+
+If you're taking over a community previously managed by someone with a high
+level of technical expertise in Matrix, it could be possible that the roles may
+not be the same. That's to say that the previous administrator could have
+deviated from the defaults[^help].
+
+## Permissions
+
+Room permissions are broken down into three types: permissions, event
+permissions, and state permissions.
+
+### Standard permissions
+
+Standard permissions include the ability to `ban` another room member, `redact`
+another room member's messages, `invite` new user's to the room, and `kick`
+members from the room. These are all fields that are _top level_ to the content
+of the `m.room.power_levels` event, and all have an associated power level.
+You can find the defaults [here](https://spec.matrix.org/latest/client-server-api/#mroompower_levels).
+
+### Event permissions
+
+Event permissions are used to encode the power level required for a user to send
+a Matrix event of a given `type`. So for example, the ability for a user to send
+most messages to a room would be `m.room.message`. These can be specified under
+the `events` field at the top level of the `m.room.power_levels` event content.
+
+If the `type` of an event cannot be found under the `events` field, then the
+power level of the `events_default` field at the top level of the
+`m.room.power_levels` event content will be used instead.
+
+### State permissions
+
+State permissions are used to encode the power level required for a user to send
+a state event of a given `type`. Usually you do not want to give users the
+ability to send state events.
+
+If the `type` of a state event cannot be found under the `events` field, then
+the power level of the `state_default` field at the top level of the
+`m.room.power_levels` event content will be used instead.
+
+## See also
+
+- [The matrix specification for `m.room.power_levels`](https://spec.matrix.org/latest/client-server-api/#mroompower_levels)
+
+[^power-levels-range]: Advanced users may use a different range.
+[^help]:
+    In that case, we recommend you to join the draupnir support room for
+    help [#draupnir:matrix.org](https://matrix.to/#/#draupnir:matrix.org).
+
+[^power-levels-spec]: The Matrix Specification for `m.room.power_levels` https://spec.matrix.org/latest/client-server-api/#mroompower_levels.