docs: make the Obtainium add link a real clickable link

Forgejo keeps obtainium:// URLs in markdown links (verified via the render API) but
not as bare autolinks — so use [text](obtainium://…) syntax in INSTALL.md and README.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

INSTALL.md

@@ -11,11 +11,13 @@ Install Obtainium from **F-Droid** or its GitHub releases:
 
 ## 2. Add BigBrainParking
 
-**Easiest — one tap:** open this link on your phone (with Obtainium installed):
+**Easiest — one tap** (on your phone, with Obtainium installed):
 
-> `obtainium://add/https://git.mowden.top/hank/BigBrainParking`
+### ➕ [Add BigBrainParking to Obtainium](obtainium://add/https://git.mowden.top/hank/BigBrainParking)
 
-It opens Obtainium's Add screen pre-filled. Tap **Add**.
+That opens Obtainium's Add screen pre-filled — just tap **Add**. (If your Markdown viewer
+strips the link, copy this into a browser on the phone:
+`obtainium://add/https://git.mowden.top/hank/BigBrainParking`)
 
 **Manual (if the link doesn't work):**
 1. Open Obtainium → **Add App**.

README.md

@@ -7,8 +7,11 @@ via **Obtainium** — no Google Play Services, no Firebase, no app store.
 ## Install it (users)
 
 BigBrainParking installs and updates through **Obtainium** — no Google Play, no account.
-**One tap** (with Obtainium installed): `obtainium://add/https://git.mowden.top/hank/BigBrainParking`
-— or follow **[INSTALL.md](INSTALL.md)** for the manual steps. Works on GrapheneOS.
+Works on GrapheneOS. On your phone (with Obtainium installed), tap:
+
+**➕ [Add BigBrainParking to Obtainium](obtainium://add/https://git.mowden.top/hank/BigBrainParking)**
+
+or follow **[INSTALL.md](INSTALL.md)** for the manual steps.
 
 ## Monorepo layout