add manual entry

docs/src/lib/functions.md

@@ -26,7 +26,7 @@ This is a list of operations that currently make use of multi-threading:
   * a transformation produces one row per group and the passed transformation
     is a custom function (i.e. not for standard reductions, which use
     optimized single-threaded methods).
-- `dropmissing` when the provided data frame has more than 1 column and `view=false` 
+- `dropmissing` when the provided data frame has more than 1 column and `view=false`
   (subsetting of individual columns is spawned in separate tasks).
 
 In general at least Julia 1.4 is required to ensure that multi-threading is used
@@ -170,6 +170,11 @@ unique
 unique!
 ```
 
+## Filtering columns
+```@docs
+findcols
+```
+
 ## Working with missing values
 ```@docs
 allowmissing