add details that Git LFS must be enabled in project

doc/workflow/lfs/manage_large_binaries_with_git_lfs.md

@@ -24,6 +24,7 @@ Documentation for GitLab instance administrators is under [LFS administration do
 ## Requirements
 
 * Git LFS is supported in GitLab starting with version 8.2
+* Git LFS must be enabled under project settings
 * [Git LFS client](https://git-lfs.github.com) version 1.0.1 and up
 
 ## Known limitations
@@ -31,10 +32,10 @@ Documentation for GitLab instance administrators is under [LFS administration do
 * Git LFS v1 original API is not supported since it was deprecated early in LFS
   development
 * When SSH is set as a remote, Git LFS objects still go through HTTPS
-* Any Git LFS request will ask for HTTPS credentials to be provided so good Git
+* Any Git LFS request will ask for HTTPS credentials to be provided so a good Git
   credentials store is recommended
 * Git LFS always assumes HTTPS so if you have GitLab server on HTTP you will have
-  to add the URL to Git config manually (see #troubleshooting)
+  to add the URL to Git config manually (see [troubleshooting](#troubleshooting))
   
 >**Note**: With 8.12 GitLab added LFS support to SSH. The Git LFS communication
  still goes over HTTP, but now the SSH client passes the correct credentials
@@ -95,7 +96,7 @@ available to the project anymore. Probably the object was removed from the serve
 
 * Local git repository is using deprecated LFS API
 
-### Invalid status for <url> : 501
+### Invalid status for `<url>` : 501
 
 Git LFS will log the failures into a log file.
 To view this log file, while in project directory:
@@ -106,6 +107,9 @@ git lfs logs last
 
 If the status `error 501` is shown, it is because:
 
+* Git LFS is not enabled in project settings. Check your project settings and
+  enable Git LFS.
+
 * Git LFS support is not enabled on the GitLab server. Check with your GitLab
   administrator why Git LFS is not enabled on the server. See
   [LFS administration documentation](lfs_administration.md) for instructions