Added issue board to word list

doc/development/documentation/styleguide/word_list.md

@@ -61,6 +61,10 @@ in the handbook when writing about Beta features.
 
 Do not use. Another option is **denylist**. ([Vale](../testing.md#vale) rule: [`InclusionCultural.yml`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/.vale/gitlab/InclusionCultural.yml))
 
+## board
+
+Use lowercase for **boards**, **issue boards**, and **epic boards**.
+
 ## checkbox
 
 One word, **checkbox**. Do not use **check box**.
@@ -120,6 +124,10 @@ Use **active** or **on** instead. ([Vale](../testing.md#vale) rule: [`InclusionA
 
 Lowercase.
 
+## epic board
+
+Lowercase.
+
 ## etc.
 
 Try to avoid. Be as specific as you can. Do not use **and so on** as a replacement.
@@ -205,6 +213,10 @@ Do not use. Use **to** instead. ([Vale](../testing.md#vale) rule: [`Wordy.yml`](
 
 Lowercase.
 
+## issue board
+
+Lowercase.
+
 ## issue weights
 
 Lowercase.