add documentation for format

docs/commands/format.md

@@ -0,0 +1,37 @@
+# format
+
+Format columns into a string using a simple pattern
+
+Syntax: `format <pattern>`
+
+### Parameters
+
+* `<pattern>`: the pattern to match
+
+## Example
+
+Let's say we have a table like this:
+
+```shell
+> open pets.csv
+━━━┯━━━━━━━━━━━┯━━━━━━━━┯━━━━━
+ # │ animal    │ name   │ age
+───┼───────────┼────────┼─────
+ 0 │ cat       │ Tom    │ 7
+ 1 │ dog       │ Alfred │ 10
+ 2 │ chameleon │ Linda  │ 1
+━━━┷━━━━━━━━━━━┷━━━━━━━━┷━━━━━
+```
+
+`format` allows us to convert table data into a string by following a formatting pattern. To print the value of a column we have to put the column name in curly brackets:
+
+```shell
+> open pets.csv | format "{name} is a {age} year old {animal}"
+━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+ # │ <value>
+───┼─────────────────────────────────
+ 0 │ Tom is a 7 year old cat
+ 1 │ Alfred is a 10 year old dog
+ 2 │ Linda is a 1 year old chameleon
+━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+```