Mention 'custom scheduling' and link to FSRS in manual

ftl/core/deck-config.ftl

@@ -346,6 +346,9 @@ deck-config-fsrs-tooltip =
     The Free Spaced Repetition Scheduler (FSRS) is an alternative to Anki's legacy SuperMemo 2 (SM2) scheduler.
     By more accurately determining when you are likely to forget, it can help you remember
     more material in the same amount of time. This setting is shared by all deck presets.
+
+    If you previously used the 'custom scheduling' version of FSRS, please make
+    sure you clear out the custom scheduling section before enabling this option.
 deck-config-desired-retention-tooltip =
     The default value of 0.9 will schedule cards so you have a 90% chance of remembering them when
     they come up for review again. If you increase this value, Anki will show cards more frequently

ts/deck-options/AdvancedOptions.svelte

@@ -34,6 +34,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         fsrs: {
             title: "FSRS",
             help: tr.deckConfigFsrsTooltip(),
+            url: HelpPage.DeckOptions.fsrs,
         },
         maximumInterval: {
             title: tr.schedulingMaximumInterval(),

ts/lib/help-page.ts

@@ -25,6 +25,7 @@ export const HelpPage = {
         newCardsday: "https://docs.ankiweb.net/deck-options.html#new-cardsday",
         dailyLimits: "https://docs.ankiweb.net/deck-options.html#daily-limits",
         audio: "https://docs.ankiweb.net/deck-options.html#audio",
+        fsrs: "http://docs.ankiweb.net/deck-options.html#fsrs",
     },
     Leeches: {
         leeches: "https://docs.ankiweb.net/leeches.html#leeches",