docs(ELI5): clarify Obsidian — optional but its own dedicated section

Promotes Obsidian from a one-line mention buried inside "Three things
to know" to a proper "What about Obsidian?" section: short answer,
what it is, decision matrix (3 user types → recommendation), 4-step
install. Required-vs-optional now explicit at the top of "What do I
need?" so beginners don't wonder whether they have to install it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kavunkarpuz-debug

ELI5.md

@@ -23,10 +23,14 @@ yours.**
 
 ## What do I need?
 
+**Required:**
 - A computer (Windows, macOS, or Linux)
 - **Python 3.10 or newer** — type `python --version` in your terminal to check
 - **Claude Code** already installed and working — type `claude --version` to check
 
+**Optional but most people install it (more on this below):**
+- **Obsidian** — a free app that makes the notebook prettier to browse
+
 That's it. No account. No cloud. No bills.
 
 ---
@@ -107,10 +111,7 @@ in any text editor. It's just text. It's just yours.
 
 If you don't like a note → delete the file. Gone.
 
-If you want to make it nicer → install **Obsidian** (free) and point it
-at the folder. Now your notes are a connected note-taking system, with
-links and graph view and search. Mnemos doesn't require this; it's just
-a free upgrade if you want one.
+(For a much nicer way to browse them, see the Obsidian section below.)
 
 ### 3. There's no AI bill
 
@@ -122,6 +123,47 @@ Your Anthropic dashboard will not show new charges from Mnemos. Ever.
 
 ---
 
+## What about Obsidian?
+
+**Short answer:** You don't need Obsidian. Mnemos works without it. But
+most people install it anyway because it makes the notebook a lot nicer
+to use, and it's free.
+
+### What is Obsidian?
+
+[Obsidian](https://obsidian.md) is a free desktop app. Point it at a
+folder of `.md` files and it shows them as a beautiful, connected
+note-taking system — with sidebar navigation, full-text search, a graph
+view of how your notes link to each other, and a clean reader.
+
+It does **not** upload anything. It does **not** need an account. It is
+just a viewer/editor for the folder you already have.
+
+### Do I need it?
+
+| You're someone who... | Obsidian recommendation |
+|---|---|
+| Just wants Claude to remember you, doesn't care about reading the notes | **Skip it.** You're done. Mnemos works fine without it. |
+| Wants to occasionally read what got written | **Optional.** Any text editor (Notepad, VS Code, TextEdit) opens `.md` files. |
+| Wants to actually browse/search/explore your memory | **Get it.** This is the experience the project was built around. |
+
+### How do I install Obsidian?
+
+1. Go to [obsidian.md](https://obsidian.md) and download for your OS
+2. Open Obsidian
+3. Click **"Open folder as vault"**
+4. Pick the same folder you gave to `mnemos init`
+
+Done. Your `Sessions/` notes now show up in Obsidian's sidebar. Click
+any wikilink (`[[like this]]`) inside a note to jump to the linked
+note. Try the **graph view** (left sidebar icon that looks like a
+constellation) — it draws every link between every Session as a map.
+
+That's the "memory palace" the project name hints at. The palace is
+just your folder; Obsidian is the lights.
+
+---
+
 ## Did something look weird?
 
 | What you saw | What happened |