v1.5.1
doc: Change link from gitiles to github
how_to_add_new_chip: Add a section for feature bits and WRSR handling
cli_client: Add rpmc command support
doc: Add favicon to config to display in the browser tab
doc: Add section about v1.5.1 into release notes
doc: Reduce size of images in docs
doc/contact: Add note to IRC section and calm down the formatting
doc: Add documentation license
doc: Add doc describing release process
doc: Convert serprog docs to rst and add to doc directory
doc: Add overview doc for user_docs
Makefile,meson.build: Add support for Sphinx versions prior to 4.x