docs: English translation updates (#190)

* docs: Add CLI article (en)

* docs: Update frames article (en)

* docs: Add article about part models (en)

* docs: Update Raspberry Pi article (en)

* docs: Remove unused raspberry3.jpg

* docs: Add COEX Pix article (en)

* docs: Add CopterHack 2019 article (en)

* docs: Update connection article (en)

* docs: Add programming overview (en)

* docs: Add anchor in modes article

* docs: Fix link in auto_setup, add editing ID (en)

* docs: Rearrange summary to match Russian version (en)

* docs/camera_frame: Add link to cli#editing (en)

* docs/wifi: Fix link to next article (en)

* docs: Add "next" links where appropriate (en)

docs/en/models.md

@@ -0,0 +1,15 @@
+# Model files for parts
+
+This page contains models and drawings of some of the drone parts. They can be used for 3D printing and/or laser cutting replacement parts.
+
+## Clever 4
+
+### Battery holder
+
+File: [`battery_holder.stl`](https://github.com/CopterExpress/clever/raw/master/docs/assets/battery_holder.stl).
+
+Filament: PLA/ABS/SBS.
+
+Infill: 50% or more.
+
+Description: the holder should be installed on the top deck. It allows the user to secure the battery with the battery strap and to mount your battery level indicator using a 3M pad.