Add append command documentation

docs/commands/append.md

@@ -0,0 +1,53 @@
+# append
+This command allows you to  append the given row to the table.
+
+**Note**: 
+- `append` does not change a file itself. If you want to save your changes, you need to run the `save` command
+- if you want to add something containing a whitespace character, you need to put it in quotation marks
+
+## Examples
+
+Let's add more cities to this table:
+
+```shell
+> open cities.txt | lines
+━━━┯━━━━━━━━━━━━
+ # │ <value>
+───┼────────────
+ 0 │ Canberra
+ 1 │ London
+ 2 │ Nairobi
+ 3 │ Washington
+━━━┷━━━━━━━━━━━━
+```
+
+You can add a new row by using `append`:
+
+```shell
+> open cities.txt | lines | append Beijing
+━━━┯━━━━━━━━━━━━
+ # │ <value>
+───┼────────────
+ 0 │ Canberra
+ 1 │ London
+ 2 │ Nairobi
+ 3 │ Washington
+ 4 │ Beijing
+━━━┷━━━━━━━━━━━━
+```
+
+It's not possible to add multiple rows at once, so you'll need to call `append` multiple times:
+
+```shell
+> open cities.txt | lines | append Beijing | append "Buenos Aires"
+━━━┯━━━━━━━━━━━━━━
+ # │ <value>
+───┼──────────────
+ 0 │ Canberra
+ 1 │ London
+ 2 │ Nairobi
+ 3 │ Washington
+ 4 │ Beijing
+ 5 │ Buenos Aires
+━━━┷━━━━━━━━━━━━━━
+```