docs: stop recommending a tmpfs over /cache

/cache holds the browser baked into the image. A tmpfs over it hides
that browser, so Byparr downloads it again on every start (the cause
behind #439). Also move shm_size and tmpfs in compose.yaml out of the
build section, where they never applied to the running container.

README.md

@@ -71,8 +71,9 @@ docker compose up -d
 > shm_size: "1gb"
 > tmpfs:
 >   - /tmp:exec,mode=1777,size=1G
->   - /cache:mode=1777,size=512M
 >```
+>
+> Do not mount a tmpfs over `/cache`: it holds the browser baked into the image, and hiding it makes Byparr download it again on every start.
 
 ### Docker install
 

compose.yaml

@@ -7,11 +7,11 @@ services:
     build:
       context: .
       dockerfile: Dockerfile
-      shm_size: "1gb"
+    shm_size: "1gb"
-    # Recommended to offload disk operations to RAM and reduce disk wear:
+    # Recommended to offload disk operations to RAM and reduce disk wear.
-      tmpfs:
+    # Leave /cache on the image: it holds the baked-in browser.
-        - /tmp:exec,mode=1777,size=1G
+    tmpfs:
-        - /cache:mode=1777,size=512M
+      - /tmp:exec,mode=1777,size=1G
     # Uncomment below to use byparr outside of internal network
     # ports:
     #   - "8191:8191"