Merge pull request #1247 from flouthoc/containerfile-docs

[CI:DOCS] docs,containerfile: `RUN --mount` mention `rw` option

docs/Containerfile.5.md

@@ -118,7 +118,7 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
               · dst, destination, target: mount destination spec.
 
-              · ro, read-only: true or false (default).
+              · ro, read-only: true (default) or false.
 
        Options specific to bind:
 
@@ -128,6 +128,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
               · from: stage or image name for the root of the source. Defaults to the build context.
 
+              · rw, read-write: allows writes on the mount.
+
        Options specific to tmpfs:
 
               · tmpfs-size: Size of the tmpfs mount in bytes. Unlimited by default in Linux.
@@ -150,6 +152,8 @@ Current supported mount TYPES are bind, cache, secret and tmpfs.
 
               · from: stage name for the root of the source. Defaults to host cache directory.
 
+              · rw, read-write: allows writes on the mount.
+
 
 **RUN Secrets**