recent_topics: Improve code level documentation.
recent_topics: Improve code level documentation.

Improved documentation of set_filter and show_selected_filters
functions.

zulip/zulip,eeshangarg/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,showell/zulip,synicalsyntax/zulip,kou/zulip,showell/zulip,synicalsyntax/zulip,punchagan/zulip,kou/zulip,kou/zulip,rht/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,shubhamdhama/zulip,rht/zulip,synicalsyntax/zulip,brainwane/zulip,synicalsyntax/zulip,eeshangarg/zulip,zulip/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,showell/zulip,synicalsyntax/zulip,andersk/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,timabbott/zulip,rht/zulip,andersk/zulip,zulip/zulip,timabbott/zulip,shubhamdhama/zulip,punchagan/zulip,brainwane/zulip,synicalsyntax/zulip,hackerkid/zulip,andersk/zulip,eeshangarg/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,timabbott/zulip,brainwane/zulip,shubhamdhama/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,brainwane/zulip,timabbott/zulip,rht/zulip,synicalsyntax/zulip,showell/zulip,shubhamdhama/zulip,andersk/zulip,timabbott/zulip,shubhamdhama/zulip,shubhamdhama/zulip,kou/zulip,rht/zulip,hackerkid/zulip,showell/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,timabbott/zulip,rht/zulip,kou/zulip,showell/zulip,eeshangarg/zulip