docs: Proofread primary key feature docs

docs/sites/features/primary-keys.rst

@@ -4,9 +4,9 @@ Primary keys
 Defining primary keys in ``dy.Schema``
 --------------------------------------
 
-When working with tabular data, it is often useful to define `primary key <https://en.wikipedia.org/wiki/Primary_key>`_. A primary key is a set of one or multiple column, the combined values of which form a unique identifier for a record in a table.
+When working with tabular data, it is often useful to define a `primary key <https://en.wikipedia.org/wiki/Primary_key>`_. A primary key is a set of one or multiple column, the combined values of which form a unique identifier for every record in a table.
 
-Dataframely supports marking columns as part of the primary key when defining a ``dy.Schema`` by setting ``primary_key=True`` on the respective columns.
+Dataframely supports marking columns as part of the primary key when defining a ``dy.Schema`` by setting ``primary_key=True`` on the respective column(s).
 
 .. note::
 
@@ -44,4 +44,4 @@ Primary keys in ``dy.Collection``
 ---------------------------------
 
 The central idea behind ``dy.Collection`` is to unify multiple tables relating to the same set of underlying entities.
-This is useful because it allows us to write `dy.filter`s that use information from multiple tables to identify whether the underlying entity is valid or not. If any `dy.filter`s are defined, ``dataframely`` requires the tables in a ``dy.Collection`` to have an overlapping primary key, i.e. there must be at least one column that is a primary key in all tables.
+This is useful because it allows us to write ``dy.filter``s that use information from multiple tables to identify whether the underlying entity is valid or not. If any ``dy.filter``s are defined, ``dataframely`` requires the tables in a ``dy.Collection`` to have an overlapping primary key (i.e., there must be at least one column that is a primary key in all tables).