Document "mute boosts" functionality (#260)

Using-Mastodon/User-guide.md

@@ -207,7 +207,7 @@ The blocked user will not be notified of your blocking them. They will be remove
 
 #### Muting
 
-If you do not wish to see posts from a particular user, but do not care about if they see your posts, you may choose to *mute* them. You can mute a user from the same menu on their profile page that you would block them from. You will not see posts from a muted user unless they @mention you. A muted user will have no way to know that you have them muted. 
+If you do not wish to see posts from a particular user, but do not care about if they see your posts, you may choose to *mute* them. You can mute a user from the same menu on their profile page that you would block them from. You will not see posts from a muted user unless they @mention you. A muted user will have no way to know that you have them muted. You can also mute a user's boosts without muting the user entirely, again from the same menu on their profile page.
 
 #### Reporting Toots or Users
 

Using-the-API/API.md

@@ -164,6 +164,13 @@ Returns the target account's [Relationship](#relationship).
 
 Returns the target account's [Relationship](#relationship).
 
+#### Muting/unmuting an account's boosts:
+
+    POST /api/v1/accounts/:id/mute_boosts
+    POST /api/v1/accounts/:id/unmute_boosts
+
+Returns the target account's [Relationship](#relationship).
+
 #### Getting an account's relationships:
 
     GET /api/v1/accounts/relationships
@@ -609,14 +616,15 @@ Note: Some attributes in the entity payload can have ``null`` value and are mark
 
 ### Relationship
 
-| Attribute                | Description                                                 | Nullable |
-| ------------------------ | ----------------------------------------------------------- | -------- |
-| `id`                     | Target account id                                           | no       |
-| `following`              | Whether the user is currently following the account         | no       |
-| `followed_by`            | Whether the user is currently being followed by the account | no       |
-| `blocking`               | Whether the user is currently blocking the account          | no       |
-| `muting`                 | Whether the user is currently muting the account            | no       |
-| `requested`              | Whether the user has requested to follow the account        | no       |
+| Attribute                | Description                                                  | Nullable |
+| ------------------------ | ------------------------------------------------------------ | -------- |
+| `id`                     | Target account id                                            | no       |
+| `following`              | Whether the user is currently following the account          | no       |
+| `followed_by`            | Whether the user is currently being followed by the account  | no       |
+| `blocking`               | Whether the user is currently blocking the account           | no       |
+| `muting`                 | Whether the user is currently muting the account             | no       |
+| `muting_boosts`          | Whether the user is currently muting boosts from the account | no       |
+| `requested`              | Whether the user has requested to follow the account         | no       |
 
 ### Report