Fix minor punctuation mistakes (#1343)

docker/README.md

@@ -50,10 +50,10 @@ Primarily, the `--premine` parameter needs to be edited to include the accounts
 
 ### Submodules
 Before deploying `polybft` environment, `core-contracts` submodule needs to be downloaded.  
-To do that simply run `make download-submodules`.
+To do that, simply run `make download-submodules`.
 
 ### Build times
-When building containers for the first time (or after purging docker build cache)
+When building containers for the first time (or after purging docker build cache),
 it might take a while to complete, depending on the hardware that the build operation is running on.
 
 ### Production