postgres: update README.md

* extended example stack.yml (set shared memory size)
      * fix incorrect link

postgres/content.md

@@ -243,7 +243,7 @@ The three easiest ways to get around this:
 
 If there is no database when `postgres` starts in a container, then `postgres` will create the default database for you. While this is the expected behavior of `postgres`, this means that it will not accept incoming connections during that time. This may cause issues when using automation tools, such as `docker-compose`, that start several containers simultaneously.
 
-Also note that the default `/dev/shm` size for containers is 64MB. If the shared memory is exhausted you will encounter `ERROR:  could not resize shared memory segment . . . : No space left on device`. You will want to pass [`--shm-size=256MB`](https://docs.docker.com/engine/reference/run/#runtime-constraints-on-resources) for example to `docker run`, or alternatively in [`docker-compose`](https://docs.docker.com/compose/compose-file/#shm_size).
+Also note that the default `/dev/shm` size for containers is 64MB. If the shared memory is exhausted you will encounter `ERROR:  could not resize shared memory segment . . . : No space left on device`. You will want to pass [`--shm-size=256MB`](https://docs.docker.com/engine/reference/run/#runtime-constraints-on-resources) for example to `docker run`, or alternatively in [`docker-compose`](https://docs.docker.com/compose/compose-file/05-services/#shm_size).
 
 ## Where to Store Data
 

postgres/stack.yml

@@ -1,11 +1,19 @@
 # Use postgres/example user/password credentials
-version: '3.1'
+version: '3.9'
 
 services:
 
   db:
     image: postgres
     restart: always
+    # set shared memory limit when using docker-compose
+    shm_size: 128mb
+    # or set shared memory limit when deploy via swarm stack
+    #volumes:
+    #  - type: tmpfs
+    #    target: /dev/shm
+    #    tmpfs:
+    #      size: 134217728 # 128*2^20 bytes = 128Mb
     environment:
       POSTGRES_PASSWORD: example