Fix some issues in polymorphic_associations.md

doc/administration/nfs.md

@@ -17,7 +17,7 @@ is recommended over NFS where possible, due to better performance.
 File system performance can impact overall GitLab performance, especially for
 actions that read or write to Git repositories. For steps you can use to test
 file system performance, see
-[File system Performance Benchmarking](operations/filesystem_benchmarking.md).
+[File System Performance Benchmarking](operations/filesystem_benchmarking.md).
 
 ## Gitaly and NFS deprecation
 

doc/development/polymorphic_associations.md

@@ -62,19 +62,19 @@ AND source_id = 13083;
 ```
 
 Here PostgreSQL can perform the query quite efficiently if both columns are
-indexed, but as the query gets more complex it may not be able to use these
-indexes efficiently.
+indexed. As the query gets more complex, it may not be able to use these
+indexes effectively.
 
 ## Mixed Responsibilities
 
-Similar to functions and classes a table should have a single responsibility:
+Similar to functions and classes, a table should have a single responsibility:
 storing data with a certain set of pre-defined columns. When using polymorphic
-associations you are instead storing different types of data (possibly with
+associations, you are storing different types of data (possibly with
 different columns set) in the same table.
 
 ## The Solution
 
-Fortunately there is a very simple solution to these problems: use a
+Fortunately, there is a solution to these problems: use a
 separate table for every type you would otherwise store in the same table. Using
 a separate table allows you to use everything a database may provide to ensure
 consistency and query data efficiently, without any additional application logic
@@ -120,8 +120,8 @@ FROM pending_group_members
 WHERE group_id = 4
 ```
 
-If you want to get both you can use a UNION, though you need to be explicit
-about what columns you want to SELECT as otherwise the result set uses the
+If you want to get both you can use a `UNION`, though you need to be explicit
+about what columns you want to `SELECT` as otherwise the result set uses the
 columns of the first query. For example:
 
 ```sql