Add initial documentation coverage for processing algorithms (#514)

documentation/how-to/processing.en.md

@@ -0,0 +1,26 @@
+---
+title: Processing Algorithms
+tx_slug: documentation_how-to_processing
+---
+
+# Processing Algorithms
+
+QField offers access to a number of processing algorithms to modify digitized features and their geometries.
+
+## Showing available algorithms
+
+Running algorithms against your features is done through the features list drawer. First, identify one or more features by tapping on the map canvas and toggle multi-selection mode by long pressing on one of the identified features. Once you've checked all features to be processed, click on the 3-dot menu and select the _Process Selected Feature(s)_ item.
+
+!![process selected features](../assets/images/process_selected_features.png "")
+
+By default, only the algorithms which are flagged as favorites will be shown. Clicking on the _All algorithms_ tab will show the full list where you can add or remove favorites.
+
+!![processing algorithms](../assets/images/processing_algorithms.png "")
+
+## Running an algorithm
+
+When an algorithm has been selected, a list of parameters will be displayed, regrouped into general and advanced ones within two distinct tabs. A third tab is available to access the algorithm's help content. For most algorithms, a live preview of the manipulated geometry will be overlayed on top of the map canvas offering an immediate feedback while parameters.
+
+!![processing parameters](../assets/images/processing_parameters.png "")
+
+Once parameters are set to your liking, click on the check button within the drawer's title bar to run the algorithm.

mkdocs.yml

@@ -93,6 +93,7 @@ nav:
       - how-to/movable-project.md
       - how-to/pg-service.md
       - how-to/plugins.md
+      - how-to/processing.md
   - Technical reference:
       - reference/index.md
       - reference/data-format.md