Add performance documentation

docs/best_practices.md

@@ -2,6 +2,17 @@ This page contains best practices when using the API to ensure the best UX possi
 
 ## Performance considerations
 
+### Only request the ContactColumns you need
+
+Each [ContactColumn]() requested via the `ContactStore#fetchContacts()` function is going to cause
+additional database queries to take place. This can cause increase loading times. It is advices to only request the ContactColumns
+you need at any given point.
+
+Keep in mind that you might have access to the information you need without requesting for any columns.
+
+If you are building a list of contacts and you need to display their names,
+use [Contact#displayName]() instead of requesting for the [ContactColumn.Names]() column. For the same scenario, use the [Contact.thumbnailUri]() instead of querying for the [ContactColumn.Image] column, if you do no need a high-res version of the contact image.
+
 ### Use a Predicate to quickly resolve phone numbers
 
 Instead of fetching all contacts' phone numbers and try to find the contact containing a phone

library/src/main/java/com/alexstyl/contactstore/ContactColumn.kt

@@ -31,7 +31,8 @@ public sealed class ContactColumn {
     /**
      * A column that will populate the [Contact.imageData] field of all queried contacts when requested.
      *
-     * @see Contact.imageData
+     *
+     * *NOTE*: You do not need this column if you do not need a high-res image of contacts. Use [Contact.thumbnailUri] instead.
      */
     public object Image : ContactColumn()
 
@@ -46,7 +47,7 @@ public sealed class ContactColumn {
      * * [Contact.phoneticMiddleName]
      * * [Contact.phoneticLastName]
      *
-     *
+     * *NOTE*: You do not need this column if you only need access to the display name of contacts (for use in a contact list for example). Use [Contact.displayName] instead.
      */
     public object Names : ContactColumn()
 

library/src/main/java/com/alexstyl/contactstore/ContactStore.kt

@@ -27,7 +27,7 @@ public interface ContactStore {
      * Returns a [FetchRequest] that emits all contacts matching the given [predicate] when collected.
      *
      * @param predicate The conditions that a contact need to meet in order to be fetched
-     * @param columnsToFetch The columns of the contact you need to be fetched
+     * @param columnsToFetch The columns of the contact you need to be fetched.
      * @param displayNameStyle The preferred style for the [Contact.displayName] to be returned. The fetched contacts' sorting order will match this option.
      */
     public fun fetchContacts(