doc: add python3-pkg-resources to build dependencies

tools/binman/control.py imports Python package pkg_resources.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/build/gcc.rst b/doc/build/gcc.rst
index 6c4b4ad..cdd7970 100644
--- a/doc/build/gcc.rst
+++ b/doc/build/gcc.rst
@@ -27,9 +27,9 @@
       device-tree-compiler dfu-util efitools flex gdisk graphviz imagemagick \
       liblz4-tool libguestfs-tools libncurses-dev libpython3-dev libsdl2-dev \
       libssl-dev lz4 lzma lzma-alone openssl pkg-config python3 \
-      python3-coverage python3-pycryptodome python3-pyelftools python3-pytest \
-      python3-sphinxcontrib.apidoc python3-sphinx-rtd-theme python3-virtualenv \
-      swig
+      python3-coverage python3-pkg-resources python3-pycryptodome \
+      python3-pyelftools python3-pytest python3-sphinxcontrib.apidoc \
+      python3-sphinx-rtd-theme python3-virtualenv swig
 
 SUSE based
 ~~~~~~~~~~