bump docker-compose.yml for the site to work with dev properly

Previously, an image built for the `build` service was then used
for `server`, and changes were invisible to the user
before the container rebuild.

After that change, the useless static `build` service is deleted,
Dockerfile is only used in the CI pipeline, and only the `server`
service is left in docker-compose for the user to test
and see documentation changes locally in real-time.

Resolves #1178

site/docker-compose.yml

@@ -1,15 +1,8 @@
 version: '2'
 services:
-  build:
-    image: remark42-site
-    build: .
-
-    volumes:
-      - ./build:/site/build
-
-  # Runs dev evn for the site
+  # Runs dev env for the site
   server:
-    image: remark42-site
+    image: remark42-site:dev
     build:
       dockerfile: Dockerfile.dev
       context: .

site/src/docs/manuals/subdomain/index.md

@@ -4,7 +4,7 @@ title: Configure Instance without Subdomain
 
 ## How to configure remark42 without a subdomain
 
-All README examples show configurations with remark42 on its own subdomain, i.e., `https://remark42.example.com`. However, it is possible and sometimes desirable to run remark42 without a subdomain, but just under some path, i.e., `https://example.com/remark42`.
+All documentation examples show configurations with remark42 on its own subdomain, i.e., `https://remark42.example.com`. However, it is possible and sometimes desirable to run remark42 without a subdomain, but just under some path, i.e., `https://example.com/remark42`.
 
 - The frontend URL looks like this: `s.src = 'https://example.com/remark42/web/embed.js;`