[i18n] Add a `make pot` command to Makefile (#3006)
[i18n] Add a `make pot` command to Makefile (#3006)

By analogy with <https://github.com/FreshRSS/FreshRSS/pull/2996>.
romibi/FreshRSS,marienfressinaud/FreshRSS,Alkarex/FreshRSS,romibi/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,aledeg/FreshRSS,aledeg/FreshRSS,aledeg/FreshRSS,romibi/FreshRSS,aledeg/FreshRSS,marienfressinaud/FreshRSS,marienfressinaud/FreshRSS,romibi/FreshRSS,marienfressinaud/FreshRSS,Alkarex/FreshRSS,Alkarex/FreshRSS,FreshRSS/FreshRSS,FreshRSS/FreshRSS,FreshRSS/FreshRSS