matrix.markdown: how should I configure my room?

TODO: I am not happy especially with the end, this will require rewrite with better time.

pages/matrix.markdown

@@ -45,6 +45,7 @@ links._
   - [How about DAG splits?](#how-about-dag-splits)
 - [Can I have a non-federated room?](#can-i-have-a-non-federated-room)
 - [What exactly is room upgrading?](#what-exactly-is-room-upgrading)
+- [How should I configure my Matrix room?](#how-should-i-configure-my-matrix-room)
 - [What are these idlekicks for inactivity, why are they for?](#what-are-these-idlekicks-for-inactivity-why-are-they-for)
   - [But the relaybots look so ugly](#but-the-relaybots-look-so-ugly)
 - [I am told that I should Matrixify my IRC channel, what does that mean?](#i-am-told-that-i-should-matrixify-my-irc-channel-what-does-that-mean)
@@ -241,6 +242,51 @@ See also [Matrix Specification on room versions](https://spec.matrix.org/latest/
 or `CTRL-F` this page for `/upgraderoom {{site.matrixLatestRoomVersion}}`
 (Element Web command to perform the upgrade).
 
+### How should I configure my Matrix room?
+
+I think there are three important questions that will each require
+consideration:
+
+- Do you want to encrypt the room?
+  - Is the room public? If so, encryption will just cause strange issues for
+    you to troubleshoot and hinder the purpouse of the channel (which you
+    should also consider).
+  - Do you want to use bridges or integrations? Unless you or someone close to
+    you is selfhosting those, they are untrusted and will defeat the point of
+    encryption, so don't encrypt.
+  - Does the room only contain trustworthy participants? Encryption may be
+    your friend.
+- Who can see the room history?
+  - If you want everyone to be able to read it, choose everyone or
+    `world_readable`.
+  - If you want everyone who has joined the room (and also crawler bots that
+    publish the history further), choose members-only or `shared`.
+  - If you want users to see the history since they were invited to the room,
+    select `invited`
+  - Otherwise select `joined` to have users only see history since they
+    joined.
+- Who can join the room? This is self-explanatory so probably everyone or
+  invited users.
+  - However my favourite rules are `knock` so that users have to ask for permission to
+    join and `knock_restricted` so users in trusted rooms can join directly
+    without knocking.
+
+Sample events for `/devtools`
+
+```json5
+// m.room.join_rules
+{
+  join_rule: "knock",
+}
+```
+
+```json5
+// m.room.history_visibility
+{
+  history_visibility: "invited",
+}
+```
+
 ### What are these idlekicks for inactivity, why are they for?
 
 Some Matrix rooms decide to connect their channel to IRC maintaining the same users on both sides, which can be heavy for the IRC network depending on bridge type of which there are three "major" variants: